If the function $f (x) = 2 x^{2} - k x + 5$ is increasing in $[1, 2]$ , then ' $k$ ' lies in the interval

(- \infty, 4)

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(4, \infty)

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(- \infty, 8]

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(8, \infty)

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Solution

The correct option is A

(- \infty, 4)

If f(x) is increasing in [1,2], then f^’(x) > 0 in the interval

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If the function f(x)=2x2−kx+5 is increasing in [1,2], then 'k' lies in the interval