Well even if you can't manage to factor them you can multiply each of the answers out to see which one is correct.

First note that there is a common factor of 2 in each term:

(so you should know automatically that c) can't be correct, right?)

Now let's take a look at .

Take the leading coefficient (1) and multiply it by the constant term (100), in this case giving us 100.

Now list all possible pairs of factors of 100:

1, 100

2, 50

4, 25

5, 20

10, 10

20, 5

25, 4

50, 2

100, 1

(and we have all the negatives as well: -1, 100 etc.)

Now find out which of these pairs add up to be the linear coefficient (20). I get that 10 + 10 = 20.

So what you want to do is to write 20x = 10x + 10x in your quadratic. So we get

Try this approach on your second problem.

-Dan