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

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)