
Patrick B. answered 01/18/20
Math and computer tutor/teacher
x(x+1) = 21
x(x+1)-21 = 0
x^2 + x - 21 = 0
x = [-1 + sqrt( 1 + 84)] / 2
= [ sqrt(85) - 1]/2
width is [sqrt(85)-1]/2
length is [sqrt(85) + 1]/2
area is [sqrt(85) - 1][ sqrt(85) + 1]/4
= [85 - 1]/4
= 84/4
= 21
so the answers in bold are correct