Question

Factor Completely: 3x2 - 21
*3(x2 - 7)?

Answer 1

Here we have
\[3x^2-21\]
\[3(x^2-7)\]
We can write
\[7= ( \sqrt 7)^2\]
so we have
\[3(x^2- (\sqrt 7)^2)\]
Can you solve now?
Use
\[a^2-b^2=(a+b)(a-b)\]

Answer 2

@Haleybob Did you try?