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

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(−$\infty$, 4) f\left( x \right) = 2 x^2 - kx + 5 f'\left( x \right) = 4x - k \text { Forf(x) to be increasing, we must have } f'\left( x \right) > 0 \Rightarrow 4x - k > 0 \Rightarrow k < 4x \text { Since x } \in \left[ 1, 2 \right], 4x \in \left[ 4, 8 \right] . \text { So, the minimum value of 4 x is 4 }. \text { Since k < 4x, k < 4 }. \Rightarrow k \in \left( - \infty , 4 \right)

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