Question

Factor completely 3x^2 − 21

Answer 1

When factor 3 out of 3x^2-21 
you  get 3(x^2-7)

Answer 2

The highest common factor of the two terms is 3, so that goes outside the bracket as 3(____). To get 3x^2, you multiply 3 by x^2, which is your first term in the bracket, and to get -21, you multiply 3 by -7, so your final answer is 3(x^2 - 7). I hope this helps!