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# C1 short question - Has me baffled Watch

1. f(x) = x^2+4kx+(3+11k) where k is a constant

1. (I have no problem with this question but i'll just mention it)
Express f(x) in the form (x+p)^2 + q, where p andq are constants to be found in terms of k.
Ans: (x+2k)^2 - 4k^2 +(3+11k)

2. (the one I have a problem with )

Given that the equation f(x) = 0 has no real roots
find the set of possible values ofk.

easy right.

b^2 - 4ac <0
therefore
4k^2 - 4(3+11k) <0
when I open up the brackets I get 4k^2 -44k - 12 <0
However, the mark scheme says I must ave 4k^2 -11k- 3 and k must be -1/4, 3

What did I do wrong?
2. The part of :

, so what is ?
3. (Original post by dnumberwang)
The part of :

, so what is ?
16k^2 0.o ?
4. (Original post by Jonario)
16k^2 0.o ?
correct.
5. And I then divide by 4 -.-
6. Thanks guys

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Updated: December 25, 2010
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