Quadratic Equations and factorized form

Question

I have trouble understanding why:

Given the equation $x^2+4x-21=0$, the solution given is $(x+7)(x-3)=0$ in its factorization form.

Using quadratic equations,

$$ x = \frac{-b\pm \sqrt{b^2-4ac}}{2a} .$$

It works out to be $x = 3$ or $x = -7.$

Answer 1

If I get what your asking, the solution is $ x=3, x=-7$. The factored form is not a solution. Try setting both factors to zero and see what you get.