Answer
$(x-7)(x-3)$
Work Step by Step
RECALL:
A trinomial of the form $x^2+bx+c$ can be factored if there are integers $d$ and $e$ such that $c=de$ and $b=d+e$.
The trinomial's factored form will be:
$x^2+bx+c=(x+d)(x+e)$
The given trinomial has $b=-10$ and $c=21$.
Note that $21=(-7)(-3)$ and $-10= (-7)+(-3)$.
This means that $d=-7$ and $e=-3$
Thus, the factored form of the trinomial is:
$[x+(-7)][x+(-3)]=(x-7)(x-3)$
