C3 Modulus 5 Marker Exam Question? (OCR) Help :(

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username2281303
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The highlighted question is the one I don't understand. (comes from the June 2016 OCR C3 maths paper)

I went through this question with the mark scheme too, and I still don't understand the correct way of answering this question.

What is the correct way of answering this question? Thank you.
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RDKGames
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(Original post by ZiggyStardust_)

The highlighted question is the one I don't understand. (comes from the June 2016 OCR C3 maths paper)

I went through this question with the mark scheme too, and I still don't understand the correct way of answering this question.

What is the correct way of answering this question? Thank you.
What's confusing?

gf(x) means g(f(x)) which is 5f(x)-4a hence 5(|2x+a|+3a)-4a

Equating this to 31a we get 5(|2x+a|+3a)-4a=31a then just solve for x
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MsMode
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Modulus can be + or - so x is either 1.5a or -2.5a.
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username2281303
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(Original post by RDKGames)
What's confusing?

gf(x) means g(f(x)) which is 5f(x)-4a hence 5(|2x+a|+3a)-4a

Equating this to 31a we get 5(|2x+a|+3a)-4a=31a then just solve for x
i solved for x using that method and got the wrong answer...
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RDKGames
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(Original post by ZiggyStardust_)
i solved for x using that method and got the wrong answer...
Then you must've tripped up in your working.
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(Original post by MsMode)
Modulus can be + or - so x is either 1.5a or -2.5a.
that's what it said in the mark scheme yeah. but i got 2 completely different answers
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Notnek
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(Original post by ZiggyStardust_)
that's what it said in the mark scheme yeah. but i got 2 completely different answers
Please post your working.
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username2281303
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(Original post by Notnek)
Please post your working.
(Original post by RDKGames)
Then you must've tripped up in your working.
after inspecting my work again, i realise i've made some rlly dumb errors, yeah.
very silly.

but thank u anyhow!
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MsMode
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(Original post by ZiggyStardust_)
that's what it said in the mark scheme yeah. but i got 2 completely different answers
So are you answers were wrong or do you want me to post my workings?
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