Scientific Calculator

Homeschool Math - Algebra, Geometry, Trigonometry, Calculus

TI-30 or equivalent. This is the basic calculator that can be used for algebra and geometry. Includes the basic functions needed such as trigonometric functions in degrees and radians, common and natural logarithms, fractions and fraction/decimal conversions, and degrees, minutes, seconds/decimal degrees conversions.


About Us

We started AskDrCallahan out of desperation!

We entered the world of homeschooling when our daughters Cassidy and Catrina were in 10th and 6th grade respectively. The leap from a private school system to schooling at home had lots of fears, but math was not one of them. I (Dale or Dr. Callahan) was serving as a professor of engineering and the University of Alabama at Birmingham, and Lea holds a masters in electrical engineering. Homeschooling high school math was the least of our problems.

Serving at the Homeschool Conference
Serving at the Homeschool Conference

But friends of ours felt differently. To them teaching high school math was a daunting task. Many of these friends asked if we would help teach math to their children as we taught it to ours. These parents recognized a lack of college level math prep and were looking for a better alternative. We agreed.

Have you ever agreed to anything not knowing what you are stepping into? In the first year we taught algebra II with trigonometry to a group of 9 kids. Things went pretty well overall.


Chaos Begins

The next year we were going to teach calculus to the same group of 9 kids, including of course our oldest Cassidy. But some families asked if we would also teach algebra II with trig again. We agreed – only then to be asked about geometry. By the third year, we were teaching algebra, geometry, algebra II with trig, calculus, biology, and physics in our basement! Something had to give.

Decision Time

We considered 3 options. 1) start a school, 2) quit altogether, or 3) create video content. I (Dale) was for quitting, but it was Lea who pushed us to go ahead and serve others by putting the content on video. So we decided to put our courses on DVD and thought we would offer them to our friends around Birmingham. We started with algebra II with trig. We recorded 8 DVDs of teaching and started a website to advertise them. People started buying. As they bought, we would burn and label the DVDs and ship them. It was just-in-time manufacturing.

Cassidy, then a college student in English, wanted to help. So we decided to tackle filming calculus. Cassidy helped to add some life to the videos. She did the direction and film editing and handled a massive amount of work in production and preparing for distribution. Now we had two products.

Customers Demand Geometry


Then customers started asking us for a course in geometry based on Harold Jacobs textbook. We said no. Then we said no again. They kept asking and we kept saying no. Finally, we thought perhaps the customer was right! (Given the fact that my true area of expertise is engineering entrepreneurship, you would think I would know better to listen to what the customers demand!)

We did a massive search at all the geometry textbooks on the market – looking for the best. (We still have a stack of geometry textbooks from many vendors in our offices!) We discovered quickly that our customers knew what they were talking about. Jacobs had done an excellent job dealing with a subject many students love to hate. So we grabbed his book and developed a course and recorded geometry to DVD. Again Cassidy played an instrumental role in producing these products, and by now we had Catrina helping in production and shipping.

When Geometry was released – it became our biggest seller overnight. Lesson here, listen to your customers. Our just in time manufacturing began to fall apart. Catrina began to beg for a solution to the new chaos. We decided to invest in other tools to develop DVDs and speed up our ability to meet demand.



Since then we have also recorded algebra based on Harold Jacobs textbook. Harold then asked us to publish his improved Solutions Manual to Algebra – which we did. However, the person you see in the algebra DVD series is Cassidy. She had developed a LOVE for math (yes – even though she was an English major). Cassidy soon developed the skill to work with younger teens to teach math and in a more entertaining and interactive way that I could ever do. The algebra course was almost 100% Cassidy!

And by now Catrina (an artist) had developed serious skills as a graphic artist, and all of our product artwork became her design. (including the cover of my book about finding your passion and loving your work – Resumes are Worthless).

The Bigger Reason We Do High School Math for Homeschoolers

When I joined the engineering faculty at UAB in 2000 I began to more clearly see the demand for engineering skills in the market. The lack of engineering talent was becoming a major issue with industry and part of a national security crisis. I begin to learn that we had more demand for engineers than we had freshmen engineering students entering into engineering school (nationwide). But, of those that entered engineering, only about 25% survived. So we had a problem of massive market demand and no one to fill the jobs. (This problem still exists today!)

I began to research and realized this was a nationwide problem. Engineering schools simply could not keep up with the demand for engineers. We simply could not get enough kids into engineering school, and those that got in often flunked out, mostly due to lack of math preparation. So I decided to investigate by contacting my math faculty at the university and asking about the failure rate. I quickly found out that students entering our the university did rather poorly in math (as a group) unless they came from one of two public high schools in the area. Those students excelled.

What made these high schools excel at teaching math? I went to find out. What I learned was shocking. High school textbook publishers water down their material because most school systems demand they water it down to improve their pass rates. These high quality public schools (and most private school) refused to use the high school material and instead used standard college level textbooks in their teaching and their teaching style.

Tim and Cassidy Cash with their boys (our grandbabies!)

Homeschool Math

Since we had started homeschooling in 2000 also, I began to see a major conflict. Most homeschool material to teach math was barely up to the normal high school standards, much less what was needed for college prep. Sure, some students were doing fine, they were going to get it no matter what. But the bulk of homeschool graduates were poorly prepared for math and STEM (science, technology, engineering, and mathematics) careers. Research nationwide backed this up.

So we were driven to provide math courses that would leave a student more than prepared to excel at math, no matter where they went to college or what they studied.

The Reality of Our Company Today

Business is a funny thing. Who you think will buy from you is rarely who becomes your customer. While we do provide courses to some in our city and state, very few of our customers are in our home town. Instead, they are all over the world. Daily we work with students and parents worldwide helping them to be ready for whatever is thrown at them in the college classroom.

Our Team

CallahanFamilySmokiesAugust2012Support. The support we offer parents and students is one of the other things that really sets us apart as a homeschool math provider. When you go with us, you are not alone. Much of our math support come from Bradley Tune – an awesome student who went through our material and constantly was asking us questions. She came on board providing much of our support in 2015.

Social Media. Lea is usually the voice (text) you hear on our Facebook site. She actively talks to and guides moms to curriculum choices we make (even in products we do not carry) and she is always looking for ways to help.


Operations: Daniel and David – our two sons have started taking an active role lately in the company also providing much of our back end office operations.

Dale Callahan: As for me (Dr. Callahan) I am still on faculty with the University. Much of my role there is working with professionals who are looking to grow their career. Much of my work is helping those smart technology people find work they love. Some change jobs, some start companies, and almost all increase their income. But more important than income, most have found their way and now their work is something they love. My podcast (Company of One) and blog deals with helping people find their way – so I get to teach at the university what I talk about in my spare time.


I am also still looking for ways to help kids understand that math is a language. Through this language, we can see the natural world around us. But —- I have also begun to look at the bigger picture. My work teaching and leading people in corporate America has made me start to question the WHY of the whole path to college. We need to be looking at the long goal. We are all created with a purpose and our WORK is how we serve God. Yet, too many of us settle, heading to college not resulting in an education to broaden us and give us potential, but instead education that often puts us in a box. With over 50% of Americans hating their job (including Christians) we know something is broken.

So a great deal of my work has become helping people find their calling and helping them to take control of their careers. That starts NOW with your homeschoolers. College is not the end game, and college does not have to put them in a box. But to get a different result takes perspective that few consider. We get caught up in the degree and the resulting career field, and then we plan to get into college. Instead, we should all be looking for where we are called. We as parents often fall in the trap of trying to fit our kids into a box as defined by what we and they know about the current career fields and job descriptions.

So while you will see more about college planning from us in the future, also be expecting to see a lot about finding your calling! And, it is not JUST for kids!

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TI Calculator Emulators

Texas Instruments (TI) are our calculators of choice. There are many other great companies – so this is a personal preference.

  • Algebra, Geometry, Biology, Chemistry  – For these courses, the TI-30 Scientific Calculator is perfect. It is inexpensive and does all you need.
  • Algebra 2 with Trig, Calculus, Physics, Statistics, and beyond – These courses require a bit more horsepower and some graphical tools. Our choice is the TI-84 Plus CE.

Note: The TI-84 Plus CE is approved for use on the following exams: PSAT, SAT, and ACT college entrance exams and AP Exams that allow or require a graphing calculator.

Web Base Calculators

Scientists and engineers are using more powerful tools today. One such tool that is FREE to use is Wolfram Alpha. It has APPS and extensions for web browsers etc. If you ask us a question on support, this is the tool we use. But, you cannot take it into the ACT/SAT or other tests – so you need to be able to use your calculator.


Emulators are software programs that operate like the calculator. While you can still find them (search the web for  “TI calculator emulators”), these are just not as important given all the other tools available.

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Algebra II with Trig Question – Is my Son Ready?

Question from a mom!

My homeschooled son struggles in high school math. He is very bright and has taken Algebra 1, Algebra 2, and Geometry with Teaching Textbooks. However, he is not a “math mind” and scored low on his yearly tests. He is going into his senior year, and I fear for his SAT/ ACT scores. He is very, very intelligent but is not a good test-taker and does not take naturally to mathematical concepts as they have been presented. How does your curriculum compare to Teaching Textbooks, and does your Algebra II/ with Trig. require that students be math geniuses already? Do you think he could be introduced to your curriculum and do well?
I am a concerned mama…I would so appreciate a detailed/ helpful review/ analysis. Thank you so much.

Answer from Dr. Callahan:

We are college based, where Teaching Textbooks are a high school-based curriculum. What does that mean? Generally, taking our stuff is much better prep for ACT/SAT and college. Does ours require genius? Not hardly. In fact, to some, it is easier because we teach concepts instead of formulas.

For instance, if you put me in a  kitchen to cook, I can do OK with a recipe. But, I do not understand cooking and food concepts well enough just to throw something together (edible). However, someone who can cook and understands stuff knows the CONCEPTS and can do well.

The ACT and SAT exams test the student’s understanding of CONCEPTS. Many students thrive on concepts but hate being put in a box of rules (recipes) which are often part of high school math. So he might be better than you think he is!

Here is what I would do in your situation.  Get ACT/SAT coaching ASAP. This will help you both determine where he stands. I would HIGHLY recommend someone who can work with him directly like Lauren (See Note the discount code!!!! He is a senior – I would do this NOW.

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Textbook Buyback

Question From Kate:

I have the textbooks and solutions manuals for Algebra I, Geometry, Algebra II and Trigonometry, and Calculus. I no longer need them and am exploring options to sell them. Do you buy textbooks?
Thank you all so much for your ministry. It was a huge blessing to me and my brother as we tackled these subjects pretty much by ourselves.

Answer from Dr. Callahan:

We do buy them, but at deep discounts. You might be better off on Ebay or Amazon. 

We buy used at these prices:

Algebra: $20(we do not buy solutions)

Geometry: $25 (We do not buy solutions)

Algebra II with Trig: $20 Solutions $5

Calculus: $10 Solutions $1

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Why McGraw-Hill Over Prentice Hall for Algebra II with Trigonometry?

Question from Kathryn: 

Is there a reason why you use McGraw-Hill over the Prentice Hall Algebra II & Trigonometry? We’re coming from Jacobs Algebra I & Geometry and I want to keep the same teaching style for my son.

Answer from Dr. Callahan:

Our view on textbooks is not to keep the same teaching style, but instead to prepare students for college and life. Therefore, our goal was to find popular college level textbooks. See
for more information on this thought.

While I am sure that having the same teaching style over and over is great for short term learning – it actually limits the students ability in the long term.

Hope this helps.


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How do DVD Instructions Correspond to Chapter Sections?

Question from Leela:

Is there a guide to know which portion of the Geometry DVD instruction corresponds to the chapter sections in the book? ie, for 6.2, when is Dr. Callahan finished with concept for that section and where does the instruction start addressing concepts in 6.3? My homeschool student needs little chunks of DVD instruction at a time; practices it, then takes the next little chunk. It’s hard to tell when the lesson is finished. Help?

Answer from Dr. Callahan:

I do not have a direct answer – but I hope this will help.

First – we cover things in groups where all the concepts are related. Not because we were lazy, but because math is concept based, and we have found people learn math better in getting the concept as a whole first and then diving into the details. So we cover related concepts at once.

Second – while this method might not seem to fit your short term goal, trust me, it is VERY helpful since the ACT and SAT exams test on conceptual thinking. Therefore, having your students get used to this kind of thinking will be preparing them to think for the exams.

But how do you deal with it? Here is what I would do….

Have them watch video on the multiple sections and then work on the individual areas or lessons. When they finish one lesson, go back and watch the video again and then do the next section of problems. This will help them see that all the concepts are the same, but the details are different.

As my wife tells me – if I were teaching someone to cook I would not lecture them on salt and have them play with salt for 3 lessons. I would explain what it does (concept) and then have them use in various ways one lesson at a time. Same idea for math. We learn better knowing the bigger why than doing the details.

I hope this helps!


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Algebra 2 with Trigonometry vs Precalculus

AskDrCallahan Calculus 1

What’s the difference between Algebra 2 with Trig and Precalculus?

Here is our view…
  • Algebra 2 with Trigonometry and Precalculus are usually the same thing with very little difference. If you put the Alg 2 with Trig book and the Precalc book by the same author/publisher side by side and compare their “Table of Contents,” you will find them almost identical.  Why do the publishers do this? Marketing. If a school requests precalc, they want to have something to offer. If they want Alg 2 with Trig, they’ve got that too. Do not miss a sale because of a cover.  While you might find some texts that differ, I would not get caught in the mud worrying about these minor differences. See below for ACT/SAT info. This marketing works fine for public/private/coop settings where the administration is setting your path. However, when homeschooling and making your own path, it can be confusing!


  • If a student takes Algebra 2 only, then they need some trig.  Students can easily do one semester in Trig using our book and videos, or even something like a Trig for Dummies book. As long as they get the basics of trig formulas, simplification of trig identities, the law of sines and cosines, and some practical uses, they are good. They can take a year to do each. Give a credit for Algebra 2 one year, and then do Trig for the next year for another credit.


  • ACT and SAT are key to college scholarship and admission. I am not saying teach to the test – but yes, teach to the test. These exams are written so the student MUST understand the material to do well – at least in the math part. This is all you need for college and for $$ for college. The big problem in college calculus is a lack of understanding of basic algebra. Students often can do the work if they see examples of like problems, but given something new, they do not know the concepts enough to make it work. So, they flunk out of college calculus.


  • Cookbook math – related to ACT/SAT we often tell people math is like cooking. I can cook a decent meal with a cookbook if I follow the instructions. However, this hardly makes me a chef since I do not understand how ingredients go together. A true cook can be let loose with ingredients and make up a delicious meal. They understand how things work. Math is like this. Too often we teach cookbook math, meaning the student can only solve a problem if formulated in the steps they have seen before. But, if thrown a real-world problem, they are lost. I realize this is not so much about Alg 2, etc – but this is a HUGE issue we see in science and engineering. We have a huge demand for people to do this kind of work, but most cannot hack it because they are cookbook math people. Good math programs teach students to think, not just calculate. Students aren’t calculators. They are created to think.

I hope all that helps you see that your student only needs one or the other – Algebra 2 with Trig or Precalculus. A rose by any other name…..

Here is a link to our recommended Scope and Sequence for high school. It will help you see a four or five-year approach to the high school level math subjects. If you have the extra year to spend, it’s okay to slow down Algebra 2 and Trig and use a year for each. If your student is late deciding to do four maths, you can do some of the math subjects in one semester. We have students that do Geometry or Trigonometry over one semester (or even summer) to get them ahead and be sure to fit in Calculus before graduation.

No need to put them through two almost identical courses. They will get frustrated and bored repeating instead of moving forward and that’s no fun for Mom either!

We hope this helps you with the Algebra 2 w/Trig vs PreCalculus confusion.
More details in The Math Problem.