Question

The length of a rectangle is 7 inches

Answer 1

Answer:

length = 20 inches

width = 13 inches

Step-by-step explanation:

l = length

w = width

area = l×w

perimeter = (2×l) + (2×w)

l = w + 7

l×w = 4×(2×l + 2×w) - 4

(w+7)×w = 4×(2×(w+7) + 2×w) - 4

w² + 7w = 4×(2w + 14 + 2w) - 4

w² + 7w = 8w + 56 + 8w - 4 = 16w + 52

w² - 9w - 52 = 0

the solution for a quadratic equation is

x = (-b ± sqrt(b² - 4ac))/(2a)

here we use now w instead of x.

and a=1

b=-9

c=-52

w = (9 ± sqrt(81 - -208))/2 = (9 ± sqrt(81+208))/2 =

= (9 ± sqrt(289))/2 = (9 ± 17)/2

w1 = (9+17)/2 = 26/2 = 13

w2 = (9-17)/2 = -8/2 = -4

and a negative length does not make any sense for a geometric shape.

so, only w1 = 13 applies.

l = w + 7 = 13 + 7 = 20