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srose
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#1
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Hi
How do I do this question:
write f(x) = x^2+6x+11 in the form (x+a)^2+b

Thanks
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Tibbles168
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#2
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Complete the square, if you still don't get it, I'll give you a clue later.
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Willis123
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#3
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#3
complete the square.

take the form x^2+ax+b

complete the square will become (x+.5a)^2-(.5a)^+b
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Necro Defain
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#4
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Here's an example: x^2 + 8x + 13 becomes (x+4)^2 - 16 + 13 = (x+4)^2 - 3, can you do it now?
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xsinfinity
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#5
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You need to complete the square.
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+epic
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#6
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(Original post by srose)
Hi
How do I do this question:
write f(x) = x^2+6x+11 in the form (x+a)^2+b

Thanks
By completing the square...
So you go (x+3)^2-9+11
then (x+3)^2+2 ---------> so a=3 and b=2

so the answer is x= -3 and 2.
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Mathematician!
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Use the general formula:

x^2 + ax + b \equiv (x+\frac{a}{2})^2 - \frac{a^2}{4} + b
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srose
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#8
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Thanks for the replies.

I understand everything apart from where the -9 comes from in:

(x+3)^2-9+11
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COMMUNIST
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#9
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f(x) = x^2+6x+11

Halve the 6x to get 3 and shove it in the brackets (x+3)

Now SQUARE 3 and put it outside the brackets. It must always be minus.

Therefore (x+3)^2 -9 and don't forget the rest of the equation:

(x+3)^2 -9 +11 becomes (x+3)^2 +2

You need to use a different method when the coefficient of x^2 > 1

Follow the example of the formula given a few posts above and you should be fine.
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srose
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#10
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Ok, Thanks I get it now
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sam161
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(Original post by Mathematician!)
Use the general formula:

x^2 + ax + b \equiv (x+\frac{a}{2})^2 - \frac{a^2}{4} + b
\frac{a^2}{4}

I thought it was just a^2?
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COMMUNIST
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(Original post by sam161)
\frac{a^2}{4}

I thought it was just a^2?
It may not always be a whole number.

E.g

x^2 -3x +4
(x-\frac{3}{2})^2 - (\frac{3}{2})^2 +4
(x-\frac{3}{2})^2 - \frac{9}{4} + 4
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matt2k8
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#13
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Look up completing the square
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heuygff
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#14
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#14
how do u square it?
where did u get 3 and the nine from. they werent even in the ques!
and if it was x^2 - 8x + 21, what wud the answer be?
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Super199
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#15
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(Original post by heuygff)
how do u square it?
where did u get 3 and the nine from. they werent even in the ques!
and if it was x^2 - 8x + 21, what wud the answer be?
Bumping a thread that is over 4 years old :eek:
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F(x)_Shadow
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#16
Thanks very much!
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............d
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#17
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Like thats gonna help no offence but this is a topic im personally struggling on and id prefer if u went itno more depth... btw sorry im not trying to be rude ,maths isnt my strong subject
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Dysf(x)al
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#18
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(Original post by ............d)
Like thats gonna help no offence but this is a topic im personally struggling on and id prefer if u went itno more depth... btw sorry im not trying to be rude ,maths isnt my strong subject
Dude this is an 8-year-old thread. Make your own thread next time.

What bit of completing the square do you struggle with?
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Sir Cumference
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#19
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Closing the thread to prevent it being bumped again.
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