Question

The length of a rectangle is 8 cm greater than its width. Find the dimensions of the rectangle if its area is 105 square centimeters. (a) Write a polynomial equation that can be solved. (b) Solve the equation by factoring (input equation with binomials in this step). (c) State solution with units *

Answer 1

Width: w

Length: w + 8

w(w + 8) = 105

w² + 8w - 105 = 0

w² + 15w - 7w - 105 = 0

w(w + 15) - 7(w + 15) = 0

(w + 15)(w - 7) = 0

w = -15, 7

width = 7cm

length = 7+8 = 15cm

Answer 2

105 = (w+8) *w

w = 7 cm

l = 15 cm

Explanation:

Area of a rectangle is

A = l*w

l = w+8

105 = (w+8) *w

Distribute

105 = w^2 +8w

Subtract 105 from each side

105-105 = w^2 +8w -105

0 =w^2 +8w -105

Factor

What 2 number multiply to 105 and add to 8

15*-7 = -105

15-7 = 8

(w+15) (w-7) =0

Using the zero product property

w+15 =0 w-7 =0

w=-15 w=7

impossible

not negative

w =7

l = 15