Answer
$x^2-4x-21=0$.
Work Step by Step
The solutions are:
$\Rightarrow x=-3$ or $x=7$
Obtain zero on one side of each equation.
$\Rightarrow x+3=0$ or $x-7=0$
Apply zero-product principle in reverse.
$\Rightarrow (x+3)(x-7)=0$
Apply FOIL method to multiply.
$\Rightarrow x^2-7x+3x-21=0$
Combine like terms.
$\Rightarrow x^2-4x-21=0$.
Hence, the quadratic equation is $x^2-4x-21=0$.
