**Question:**

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.