Posted by **Alex** on Sunday, February 4, 2007 at 12:38pm.

1.3x^2+17x+10

2.5y^8-125

3.a^2-2ab-15b^2

*Please help me.You have to factor by completing.

Let's look at #1:

3x^2 + 17x + 10

We have 2 and 5 as factors of the last term.

What combinations can we do to arrive at the middle term?

(3x + ?)(x + ?)

Let's try (3x + 5)(x + 2), which will be 3x^2 + 11x + 10. This is not what we want.

Let's try (3x + 2)(x + 5), which will be 3x^2 + 17x + 10. This IS what we want; therefore, we have found the factors of this trinomial.

Here's a few hints for the other two.

Hint for #2: First factor out 5. Then factor what's left.

Hint for #3: First factor (a - 5b). Can you determine the second factor?

I hope this will help.