# Talk

## Help Year 9 maths

(25 Posts)
Thisisconfusing Mon 30-Oct-17 18:16:49

DS has got stuck on this maths Question. For the first time I realise that I don't know how to help him! Any help so we can both work out how to do it gratefully received . Obviously I will ask DS to ask teacher but knowing him he probably won't get around to asking - and I'm curious too ! Thanks in advance .

Solve the equation :

3 4 5x
_ = _________
x+3 x-3 x squared - 9

Sorry don't know how to do the x squared symbol ! Hope the question is clear . Thanks

Thisisconfusing Mon 30-Oct-17 18:17:52

Whoops sorry the question has not posted clearly - I will try and set it out properly !

Snap8TheCat Mon 30-Oct-17 18:19:09

Take a photo

Thisisconfusing Mon 30-Oct-17 18:24:56

Yes new to mumsnet so my first post but couldn't figure out how to that - I'm having a quick look now

Thisisconfusing Mon 30-Oct-17 18:37:10

I think I'm being pretty dim here but I just can't seem to work out how you post a photo on this particular thread. I will be back when I've worked it out! If anyone would like to enlighten me in the meantime I would be very grateful !

booellesmum Mon 30-Oct-17 18:38:57

Can you click the paperclip/attach icon at the bottom and then choose camera option to take a photo?

Thisisconfusing Mon 30-Oct-17 18:52:16

Thanks Maybe it doesn't work for a mobile - I just can't see an attach icon or paper clip ! I feel that attaching a photo must be very easy to do and I'm just not seeing it! Oh dear ....

AssassinatedBeauty Mon 30-Oct-17 18:53:41

Are you using the app or the mobile website?

Thisisconfusing Mon 30-Oct-17 19:57:59

Mobile .

Snap8TheCat Mon 30-Oct-17 20:20:38

Under the box you are typing in, click the paper clip icon.

Thisisconfusing Mon 30-Oct-17 20:22:06

app downloaded - photo of question now attached. Thank you in advance

SearchingforSleep Mon 30-Oct-17 22:11:17

Sorry, this is probably a bit late but in case it's any help, I think you multiply each item in the equation by (x+3)(x-3). So you can then do a bit of cancelling out and a much simpler bit of algebra to solve drops out. (Expanding out the brackets of (x+3)(x-3) gives x^2 -9 so that cancels out too on the right hand side.) Does that make sense? I can attempt a slightly more coherent explanation if needed - I'm very rusty!

mineofuselessinformation Mon 30-Oct-17 22:25:42

Hope this helps...
It's 'difference of two squares (DOTS)':
I missed a step out (1). (2) then carries on after.
Hope that makes sense!

mineofuselessinformation Mon 30-Oct-17 22:27:01

Just realised the (2) is missed off on the right hand side, but the arrow shows where it is....

Thisisconfusing Mon 30-Oct-17 22:32:20

Oh yes - I can see that now! Thank you very much Searching for your reply that does make sense

PickleFish Mon 30-Oct-17 22:34:33

yes, agree, but I'd reduce the final answer to -7/2

(You can then check it by substitution, and both sides work out to -70/13 )

Thisisconfusing Mon 30-Oct-17 22:36:49

And thank you mines too - since I've got -3.5 from the hint given by Searching so that your workings confirms I've understood . I'm way too rusty - My last maths lesson was in 1984!

Thisisconfusing Mon 30-Oct-17 22:37:22

Thank you all !

MummySparkle Mon 30-Oct-17 22:43:09

Okay, so fractions you always need to do the same to top and bottom & you need a common denominator at the bottom to simplify the two on the left hand side.

So you get:

3(x-3)/(x+3)(x-3) - 4(x+3)/(x+3)(x-3) = 5x / x^2 -9

Then multiply that all out gives you
3x-9/ x^2 -9 - 4x +12/x^2 -9 = 5x/x^2 -9

Now because x^2 -9 is at the bottom of all of the fractions you can multiply everything by x^2 -9 to be left with:

3x - 9 - 4x -12 = 5x

(Note that it becomes -12 because you are subtracting (4x + 12)

Collect like terms:
-x -21 = 5x

Add x to both sides

-21 = 6x

Divide by 6:

-3.5 = x

Fluffysparks Mon 30-Oct-17 22:47:50

Tbh if your DS can’t work it out you shouldn’t be doing it for him, as it will just mean his teacher assumes he can do the sum. Also, isn’t that rather simple for Y9?

Thisisconfusing Tue 31-Oct-17 00:08:56

Maybe it is Fluffy. I really wouldn't know - tbh he probably wasn't focussing since it was the holidays. He's normally ok at maths and it's the first time he's actually asked me about something! And it bugged me that I couldn't remember how to do it.

And agreed Fluffy if it were homework to be handed in . But it was just some practice revision questions in advance of a test. So it won't be marked or anything .

noblegiraffe Tue 31-Oct-17 00:34:14

isn’t that rather simple for Y9?

No.

MummySparkle Wed 01-Nov-17 00:30:04

Fluffy I thought the OP was more interested in how To do it as opposed to the answer so that she can answer it and maybe use the same technique on the next question.

As for it being simple for year 9? Not really. I’ve worked with some y9 students who barely knew there times tables right through to those who would have whizzed through this without a second thought. Maths in particular is a subject that everyone has to approach at their own speed, hence the importance of maths sets ASAP in secondary.

csa26 Wed 01-Nov-17 00:38:36

None of my Yr 11 students (I'm a tutor) spot D.O.T.S. questions - I really have to drum it into them to look out for [square number] - [square number]. And all but the most mathematically able ask for help with algebraic fractions even if it isn't a sneaky D.O.T.S. question. So no, definitely not easy for Yr 9!

MummySparkle Wed 01-Nov-17 00:48:40

I was a maths tutor & TA in a secondary maths department & I still don’t really get what DOTS means but I do know how to work them out. I vaguely remember the lesson we were taught it where my teacher kept going on about it being a shortcut. It just made more sense to me to do the math!

Join the discussion

Registering is free, easy, and means you can join in the discussion, watch threads, get discounts, win prizes and lots more.

Register now »