Question

In a parallelogram whose area is 15, the base is represented by x+7 and the altitude x-7. Find the base of parallelogram.

Answer 1

Area = (base)*(height)
15 = (x+7)(x-7)
(x+7)(x-7) = 15
x^2 - 49 = 15
x^2 - 49+49 = 15+49
x^2 = 64
sqrt(x^2) = sqrt(64)
x = 8 ... note that x can't be negative

If x = 8, then the base is...
x+7 = 8+7 = 15

Therefore the base is 15 units. 
(the height is x-7 = 8-7 = 1 unit)