Why does the perimeter not vary directly with it’s length (when the length changes)
Answer from Dr. Callahan:
If you look at the formula for perimeter is becomes
P = 2x + 6
We see it is linear,
y = ax + b
but a direct variation is a subset of linear where the b =0 (see page 85)
This is a minor definition you will rarely see – so from now on just expect Linear or not.