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The coefficient of x^3 in the expansion of (2+x)(3-ax)^4 is 30. Find the values of th

The coefficient of x^3 in the expansion of (2+x)(3-ax)^4 is 30. Find the values of the constant a. I understand but do not know how to do it. Working would be appreciated!!
Reply 1
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BabyMaths
Original post by SophieL1996
The coefficient of x^3 in the expansion of (2+x)(3-ax)^4 is 30. Find the values of the constant a. I understand but do not know how to do it. Working would be appreciated!!


Yes, working would be appreciated.

What have you done?
Reply 2
Avatar for SophieL1996
SophieL1996
OP
2
I expanded using the x^3. amd then timesd it by (2+x)
Reply 3
Avatar for Dalilsp
Dalilsp
9
errr wut?

First ignoring the first set of brackets, expand the (3-ax)^4 up to the x^4.

Simplify.

Multiply each term with (2+x).

Simplify.

Find coefficient of x^2.

===================

No one will show you working without you showing us that you have made a valid attempt at the question and are genuinely stuck with the question and is interested in finding out how to do the question instead of wanting to finish your homework as soon as possible.
Reply 4
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BabyMaths
Original post by SophieL1996
I expanded using the x^3. amd then timesd it by (2+x)


Show us?
Reply 5
Avatar for SophieL1996
SophieL1996
OP
2
Original post by Dalilsp
errr wut?

First ignoring the first set of brackets, expand the (3-ax)^4 up to the x^4.

Simplify.

Multiply each term with (2+x).

Simplify.

Find coefficient of x^2.

===================

No one will show you working without you showing us that you have made a valid attempt at the question and are genuinely stuck with the question and is interested in finding out how to do the question instead of wanting to finish your homework as soon as possible.


Thanks I will have a try, and it is not homework, I am revising questions that I am not very good at and need help with.
Reply 6
Avatar for SophieL1996
SophieL1996
OP
2
Original post by BabyMaths
Show us?


No need. Someone private messaged me showing all the working. :biggrin:
Reply 7
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BabyMaths
Original post by SophieL1996
No need. Someone private messaged me showing all the working. :biggrin:


And you think they helped you. :facepalm:
In maths, we don't learn via memorising answers but knowing how the steps interlink with each other and applying it in various different situations.

Your call though, OP.
Reply 9
Avatar for SophieL1996
SophieL1996
OP
2
Original post by SecretDuck
In maths, we don't learn via memorising answers but knowing how the steps interlink with each other and applying it in various different situations.

Your call though, OP.


sorry who was that a reply to ?
Original post by SophieL1996
sorry who was that a reply to ?


You, OP.
Reply 11
Avatar for SophieL1996
SophieL1996
OP
2
Original post by SecretDuck
You, OP.


Fo. All I needed was a little help and everyone is getting bitchy about it. Pathetic.
Original post by SophieL1996
Fo. All I needed was a little help and everyone is getting bitchy about it. Pathetic.


I always attempt the question and then ask for help if I'm really stuck and show all my working. Then I'm corrected on any mistakes.

This is how the maths forum works :smile:
Reply 13
Avatar for Dalilsp
Dalilsp
9
Don't blame us -> you never showed any working, hence showing no proof that you actually wanted help rather than a quick answer. Its usually the etiquette that decent people show on this forum when asking for help.
Reply 14
Avatar for Dalilsp
Dalilsp
9
Who really gives a damn about negative ratings?

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