Question

what about 9g^2+21gs+10s^2?

Answer 1

To factor multiply outside coefficients 9*10 = 90
look for factors of 90 that add up to 21
2*45
3*30
6*15
9*10

6+15=21
(9g +6s)(9g+15s)
reduce
(3g+2s)(3g+5s)