Question

How do work this out

Answer 1

We can factor this by using grouping. Take the leading coefficient and multiply it by the constant. In this case we get 5*-7 = -35. 

Now we need 2 numbers that add to 2 and multiply to be -35. The numbers are -5 and 7.

So split the 2r into these two terms and group.

(5r^2 - 5r) + (7r - 7)

Factor both groups.

5r(r-1) + 7(r-1)

The factors of (r-1) can be added together to get the answer.

(r-1)(5r+7)