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Application of Derivatives — Maths STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceMathsApplication of Derivatives1 Mark
MCQ
If the function $f(x)=2 x^2-k x+5$ is increasing on $[1,2]$, then $k$ lies in the interval:
  • ✓
    $(-\infty,4)$
  • B
    $(4,\infty)$
  • C
    $(-\infty,8)$
  • D
    $(8,\infty)$
✓

Answer

Correct option: A.
$(-\infty,4)$
$f(x)=2 x^2-k x+5$
$f^{\prime}(x)=4 x-k$
$f(x)$ is increasing
$4 x-k<0$ on $[1,2]$
$k<4 x$
Minimum value of $k$ is $4$ .
$k<4$
$\text{k}\in(-\infty,4)$

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