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Math question help! Expanding and simplifying

So I’m practicing the aqa higher maths paper 1 from this years exam, and I have completed a question but not sure if I have it right or not, so any help would be appreciated. (The marks available are /4)

Question: “Expand and simplify (x -4)(2x +3y)^2

I’ll first show my workings out, then my answer:

(x -4)(2x +3y)^2

(2x +3y)^2 = (2x +3y)(2x +3y)
= 4x + 6xy + 6xy + 9y
= 4x + 12xy + 9y

(x -4)(4x +12xy +9y)
= 5x +13yx +9xy -16 -48 -36

ANSWER I GOT: = 5x + 22y - 100

Have I got it right? If not where did I go wrong? And how much marks would I of got for this?

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Moving to Maths :smile: tagging in someone I know can help!


@Protostar
Reply 2
Avatar for iwant2die
iwant2die
OP
14
Original post by Paracosm
Moving to Maths :smile: tagging in someone I know can help!


@Protostar


Thank you!! :smile:
Reply 3
Avatar for Aweevee
Aweevee
11
Why dont you search up the mark scheme for the exam paper
2x x 2x = 4x^2, not 4x :smile:
Original post by iwant2die

(2x +3y)^2 = (2x +3y)(2x +3y)
= 4x + 6xy + 6xy + 9y


(3y)(3y)=9y2≠9y(3y)(3y)=9y^2 \neq 9y, similarly for (2x)(2x)(2x)(2x)
Original post by iwant2die
So I’m practicing the aqa higher maths paper 1 from this years exam, and I have completed a question but not sure if I have it right or not, so any help would be appreciated. (The marks available are /4)

Question: “Expand and simplify (x -4)(2x +3y)^2

I’ll first show my workings out, then my answer:

(x -4)(2x +3y)^2

(2x +3y)^2 = (2x +3y)(2x +3y)
= 4x + 6xy + 6xy + 9y
= 4x + 12xy + 9y

(x -4)(4x +12xy +9y)
= 5x +13yx +9xy -16 -48 -36

ANSWER I GOT: = 5x + 22y - 100

Have I got it right? If not where did I go wrong? And how much marks would I of got for this?


Hi - this isn’t quite right as you’re not expanding properly.

Could you tell me what xx multiplied by xx is? :smile:
2x *2x is 4x^2
i think you've just missed out some of the squared notations?
(edited 6 years ago)
Reply 9
Avatar for iwant2die
iwant2die
OP
14
Original post by Protostar
Hi - this isn’t quite right as you’re not expanding properly.

Could you tell me what xx multiplied by xx is? :smile:


x multipled by x is x^2?
Reply 10
Avatar for iwant2die
iwant2die
OP
14
Original post by basbousa
urm you should expand the second bracket fully and then multiply thst out by the first bracket


That’s what I did?
Original post by iwant2die
So I’m practicing the aqa higher maths paper 1 from this years exam, and I have completed a question but not sure if I have it right or not, so any help would be appreciated. (The marks available are /4)

Question: “Expand and simplify (x -4)(2x +3y)^2

I’ll first show my workings out, then my answer:

(x -4)(2x +3y)^2

(2x +3y)^2 = (2x +3y)(2x +3y)
= 4x + 6xy + 6xy + 9y
= 4x + 12xy + 9y

(x -4)(4x +12xy +9y)
= 5x +13yx +9xy -16 -48 -36

ANSWER I GOT: = 5x + 22y - 100

Have I got it right? If not where did I go wrong? And how much marks would I of got for this?


You messed up your expanding. I don't know what the mark scheme says but most likely 1/4, possibly 2.

When you multiplied out (2x +3y)(2x +3y), you got the first term as 4x. 2x times 2x is 4x^2. Same goes for the y term. So you should have gotten 4x^2 + 12xy + 9y^2.

When you then multiply that by (x-4), again you need to use ^2 and ^3. You should end up with 6 terms once you finish simplifying.
Original post by iwant2die
x multipled by x is x^2?


Indeed. So 2x2x multiplied by 2x2x would therefore be?
Reply 13
Avatar for iwant2die
iwant2die
OP
14
Original post by Protostar
Indeed. So 2x2x multiplied by 2x2x would therefore be?


4x^2? I guess that’s where I messed up
Original post by iwant2die
4x^2? I guess that’s where I messed up


You got it :smile: and the same with your yys. Redo it and post what you end up with?
Reply 15
Avatar for iwant2die
iwant2die
OP
14
Original post by Protostar
You got it :smile: and the same with your yys. Redo it and post what you end up with?


Okay! Thank you :smile:
Reply 16
Avatar for iwant2die
iwant2die
OP
14
Original post by Protostar
You got it :smile: and the same with your yys. Redo it and post what you end up with?


I did this bit again: (x -4)(4x +12xy +9y)

Answer I got this time: 4x^2 +12x^2y +9xy -16x -48xy -36y

Is this the final answer or do I do anything from here? Or have I messed up again?
Original post by iwant2die
I did this bit again: (x -4)(4x +12xy +9y)

Answer I got this time: 4x^2 +12x^2y +9xy -16x -48xy -36y

Is this the final answer or do I do anything from here? Or have I messed up again?


Your first error was right at the start, trying to multiply the double bracket - can you see you’ve gone from 4x24x^2 back to 4x4x? Start the whole question again I think :smile:
Reply 18
Avatar for iwant2die
iwant2die
OP
14
Original post by Protostar
Your first error was right at the start, trying to multiply the double bracket - can you see you’ve gone from 4x24x^2 back to 4x4x? Start the whole question again I think :smile:


Wait, so for double bracket bit: (2x +3y)(2x +3y) would it be = (4x^2 + 12xy +9y^2) because:

2x times 2x = 4x^2
2x times 3y = 6xy
3y times 2x = 6xy (the two 6xy would make 12xy)
3y times 3y = 9y^2

Is this correct for this bit? (Sorry if I’m being annoying)
Original post by iwant2die
Wait, so for double bracket bit: (2x +3y)(2x +3y) would it be = (4x^2 + 12xy +9y^2) because:

2x times 2x = 4x^2
2x times 3y = 6xy
3y times 2x = 6xy (the two 6xy would make 12xy)
3y times 3y = 9y^2

Is this correct for this bit? (Sorry if I’m being annoying)


That’s it :biggrin: now carry on with the rest of it and you’ll get there!

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