Question

factor the trinomial, or state that the trinomial is prime.
$y^2 - 10y + 21$

select the correct choice below and, if necessary, fill in the answer box within your choice.
a. $y^2 - 10y + 21 = \square$
b. the polynomial is prime.

Explanation:

Step1: Find factors of 21

We need two numbers that multiply to $21$ and add to $-10$. These numbers are $-7$ and $-3$, since $(-7)\times(-3)=21$ and $(-7)+(-3)=-10$.

Step2: Factor the trinomial

Rewrite the trinomial using the found factors in the form $(y+a)(y+b)$.
$y^2 -10y +21=(y-7)(y-3)$

Answer:

A. $y^{2}-10y + 21=(y-7)(y-3)$