MHB Find Area Formula of Rectangle

[mathdad]

Let x denote the width of a rectangle with perimeter 30 feet. Find the area of this rectangle.

Let me see.

P = 2L + 2W

30 = 2L + 2x

(30 - 2x) = 2L

(30 - 2x)/2 = L

A = LW

A = [(30 - 2x)/2]x

Correct?

I guess we can simplify a little more.

A = x(15 - x)

Correct?

 

[skeeter]

yes ... the length & width of a rectangle sum to half the perimeter

$P = 2(L+W) \implies L+W = \dfrac{P}{2}$

 

[mathdad]

Good to be right.