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completing square- help

2x-8x^2X+10?
Reply 1
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Reply 2
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Reply 3
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Original post by hgjki
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Rearrange to get in ax^2+bx+c
Factor out a
Then complete the square as normal
Reply 5
Original post by 12ksmith
Rearrange to get in ax^2+bx+c
Factor out a
Then complete the square as normal


yh i did that
So what's the problem?
Original post by hgjki
yh i did that


So what's the problem?
Reply 8
Original post by 12ksmith
So what's the problem?


2x-8x^2+10
8x^2-2x+10
2(4x^2-1x)+10
????????
Reply 9
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First you have rearranged incorrectly. It should be -8x^2 +2x +10

Then you need to factor out -8 not 2 so that the coefficient becomes 1. Meaning you can complete the square as normal. If you can't do that - go do some questions where the coefficient of x squared is 1.
Reply 11
Original post by 12ksmith
First you have rearranged incorrectly. It should be -8x^2 +2x +10

Then you need to factor out -8 not 2 so that the coefficient becomes 1. Meaning you can complete the square as normal. If you can't do that - go do some questions where the coefficient of x squared is 1.


Thanks
Original post by hgjki
2x-8x^2+10
8x^2-2x+10
2(4x^2-1x)+10
????????


Where has the minus gone?

Try:

-2{4x^2 -x - 5] which also still hasn't got x^2 coeff of 1 so ...
Reply 13
Original post by Muttley79
Where has the minus gone?

Try:

-2{4x^2 -x - 5] which also still hasn't got x^2 coeff of 1 so ...


Oh my teacher told me to put the 10 outside the bracket?
Original post by hgjki
Oh my teacher told me to put the 10 outside the bracket?


OK - you can do that but you do need to think about the sign ... you can't just change the sign of two terms.

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