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
