factor:

9y^2 - 225

Question

factor:

9y^2 - 225

anonymous · Answer

(3y-15)(3y+15)

anonymous · Answer

Thanks!

mertsj · Answer

NO!!  First factor out the 9

anonymous · Answer

which is 3

mertsj · Answer

$$9(y^2-25)=9(y-5)(y+5)$$

anonymous · Answer

then 15 * 15 = 225

anonymous · Answer

This is called a difference in squares, the two squares being 3y and 15:
(3y)^2 = 9y^2
15^2 = 225
when we see that there is a minus sign between them, we can always factor them like so:
(3y + 15)(3y - 15)
This works because if we use the foil method, 3y on the left side gets multiplied by -15 on the right which = -45y, but then 3y on the right side gets multiplied by 15 on the left side which equals a positive 45y and so they cancel out.

anonymous · Answer

You can factor 3 out from the factors I showed. Same thing.

anonymous · Answer

so which answer is correct i thought GT is correct

anonymous · Answer

Right then you factor out the 3 from both binomials, or it would be easier to factor out the 9 first

mertsj · Answer

9(y-5)(y+5) is the correct answer.

anonymous · Answer

you can do it both ways and get the same answer, but it saves a little bit of time if you go ahead and factor the 9 out

mertsj · Answer

Any teacher worth his/her salt will teach that the first step in factoring anything is to remove the GCF

anonymous · Answer

9(y-5)(y+5) are very good set of factors. Let us not argue about correctness. :)