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# factorising help

1. Hi,

I am struggling to answer this question

6y(x+3y)+9(x+3y)^2

I don't know how to fully expand this and factorise.

help
2. You have two terms: 6y(x+3y) and 9(x+3y)^2. To factorise, you need to look for common factors in both terms. 3 and (x+3y) are common factors so you can take them outside the expression. So you'll have this:

3(x+3y)( ...... )

Can your work out what will go inside the brackets?
3. (Original post by notnek)
You have two terms: 6y(x+3y) and 9(x+3y)^2. To factorise, you need to look for common factors in both terms. 3 and (x+3y) are common factors so you can take them outside the expression. So you'll have this:

3(x+3y)( ...... )

Can your work out what will go inside the brackets?
No the way I have been taught is to expand the brackets and then do it
4. (Original post by zed963)
No the way I have been taught is to expand the brackets and then do it
5. (Original post by zed963)
No the way I have been taught is to expand the brackets and then do it
Sometimes it is useful to expand and then factorise but not in this case. Expanding this expression will make it harder to factorise and that could be the reason why you're having trouble with the question.

I'm pretty sure that your teacher would expect you to factorise using the method I showed in my last post.
6. (Original post by zed963)
No the way I have been taught is to expand the brackets and then do it
You appear to have been taught 'wrong'. ALWAYS try and factorise by using the highest common factor. In this case the obvious factors to 'go outside' are 3(x+3y)
7. (Original post by zed963)
No the way I have been taught is to expand the brackets and then do it
Wow you have a retarded teacher.

Take a factor of (x+3y) from every term so you get (x+3y)(6y+9(x+3y))
Expand within the second bracket and collect the terms. Another factor can be taken out and that is 3, from the second bracket only.
8. (Original post by uttamo)
Wow you have a retarded teacher.
I would not be so quick to criticise the teacher in this case

(Original post by zed963)
I don't know how to fully expand this and factorise.
help

Do not suggest that you have not been shown how to factorise these as we spent A LOT of time on them with you last weekend

When you still did not understand we said that you should seek personal help at school

So I ask again ... HAVE YOU?

Before people waste too much time

http://www.thestudentroom.co.uk/show....php?t=1969289
9. (Original post by TenOfThem)
I would not be so quick to criticise the teacher in this case

Do not suggest that you have not been shown how to factorise these as we spent A LOT of time on them with you last weekend

When you still did not understand we said that you should seek personal help at school

So I ask again ... HAVE YOU?

Before people waste too much time

http://www.thestudentroom.co.uk/show....php?t=1969289
10. (Original post by zed963)
11. (Original post by TenOfThem)
12. (Original post by zed963)
Good

You need someone to sit down with you on this
13. (Original post by zed963)
Here is one way that might help. Let A = x + 3y
Attached Images

14. (Original post by steve2005)
Here is one way that might help. Let A = x + 3y

15. (Original post by TenOfThem)
I would not be so quick to criticise the teacher in this case
Yeah you're right lol I take it back
16. So how would I do 50(2x+1)^2-18(1-x)^2
17. (Original post by zed963)
So how would I do 50(2x+1)^2-18(1-x)^2
I would use the difference of 2 squares

Spoiler:
Show

Spoiler:
Show
2(13x+2)(7x+8)

It might be easier for you to expand and simplify
18. (Original post by TenOfThem)
I would use the difference of 2 squares

It might be easier for you to expand and simplify
? I didn't understand what u meant
19. (Original post by zed963)
? I didn't understand what u meant
That's why she suggested that YOU should expand the brackets first.
20. So would it be 200x+1 -18-18x^2

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