How do I solve x sq + (x + 21)sq = 51sq?

Question

It needs to fit into the quadratic equation

Answer 1

expand the (x+21)²

x² + (x+21)² = 51²
x² + x² + 42x + 441 = 2601
2x² + 42x - 2160 = 0
x² + 21x - 1080 = 0
(x+45)(x-24) = 0
x = -45 or x = 24

Answer 2

x^2 + (x+21)^2 = 2601
x^2 + (x+21)(x+21) - 2601 = 0 [Now, FOIL the middle part so...]
x^2 + x^2 + 42x + 441 - 2601 = 0
2x^2 +42x - 2160 = 0
Doesn't that look like the quadratic equation?

Answer 3

foil the binomial and move everything to one side, combining like terms so you have a quadratic equation