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Question

If f(x)=x2+kx+1 is monotonic increasing in [1,2] then the minimum values of k is-

A
4
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B
4
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C
2
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D
2
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Solution

The correct option is D 2
f(x)0 for monotonically increasing.
2x+k0
k2x
Now it is increasing in the interval [1,2]
Hence
k2 and k4
Hence
From both we get
k2
Hence minimum value of k is 2

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