Factor by grouping

Question

3s²-7s-21s+49

Answer 1

When you factor by grouping, you want to factor sets of terms separately, then see if they have anything in common after that. With 4 terms, you look at each group of two separately:

 

What is the common factor between 3s² - 7s ? s is all they have in common, so we factor it out

s(3s-7)

 

Do the same for -21s+49. This is a little trickier, since the 21s is negative. They have 7 in common, but you should factor out a -7 to make the first of these two terms positive:

-7(3s-7)

 

If you combine these in one expression again you have

s(3s-7)-7(3s-7)

 

Both terms now have (3s-7) in common, you can factor it out to get

(3s-7)(s-7)

 

If you're unsure about anything here, please ask!