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Maths unit 2 - factorising

Hi im trying to simplify x(squared)-2x-15/x(squared) -4x-21.
So far i have factorised the bottom to be (x+7)(x-3), is this right?
Also please could I have a little help factorising the top because I'm struggling with what two numbers multiply to get 15x(squared) but add to get 2x.
Thanks!!:smile:
Answer is in spoilers...

Spoiler

(edited 11 years ago)
Original post by Dougieowner
Hi :biggrin:

The bottom is (x+7)(x-3), correct.

It needs to add to make -2x and multiply to make -15.

Factors of -15:
1 and -15
5 and -3

We see here that -5 and 3 would multiply to make -15, but still add to make -2x.

So: (x+3)(x-5)

This means it is:

(x+5)(x-3) / (x+7)(x-3)

(x-3) is on both the top and bottom, so that therefore cancels out.

So the answer should be:

x+5 / x+7

(I think. If I've got it wrong someone else will give an answer...)


I would edit your post to spoiler it :tongue:

just put [ spoiler ] text here [ /spoiler ] (remove the spaces though)

Otherwise you could get warning points - you wouldn't believe how many times mods have given me points for it
Reply 3
Avatar for Notnek
Notnek
21
Original post by gracelily96
Hi im trying to simplify x(squared)-2x-15/x(squared) -4x-21.
So far i have factorised the bottom to be (x+7)(x-3), is this right?
Also please could I have a little help factorising the top because I'm struggling with what two numbers multiply to get 15x(squared) but add to get 2x.
Thanks!!:smile:

For future questions you should post in the maths study help forum:

http://www.thestudentroom.co.uk/forumdisplay.php?f=38
Reply 4
Avatar for Notnek
Notnek
21
Original post by The Polymath
I would edit your post to spoiler it :tongue:

just put [ spoiler ] text here [ /spoiler ] (remove the spaces though)

Otherwise you could get warning points - you wouldn't believe how many times mods have given me points for it

I'm not sure if that would happen here since those rules aren't part of this particular subforum :smile:
Original post by The Polymath
I would edit your post to spoiler it :tongue:

just put [ spoiler ] text here [ /spoiler ] (remove the spaces though)

Otherwise you could get warning points - you wouldn't believe how many times mods have given me points for it


Thanks for letting me know, I had no idea. :L

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