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Mathematics · 2026 · 2 marks
CBSE 2026 · Region 3 · Set 1 · Q22
Find the sub-interval(s) of (0, (π)/2) in which f ( x )= tan x -4 x is increasing.
Find the sub-interval(s) of $\displaystyle \left(0, \frac{\pi}{2}\right)$ in which $\displaystyle \mathrm{f}(\mathrm{x})=\tan \mathrm{x}-4 \mathrm{x}$ is increasing.
Marking-scheme solution
$\displaystyle \mathrm{f}^{\prime}(x)=\sec^{2} x-4$
Put $\displaystyle \mathrm{f}^{\prime}(x)=0 \Rightarrow x=\dfrac{\pi}{3}$
Hence f is increasing in $\displaystyle \left(\dfrac{\pi}{3}, \dfrac{\pi}{2}\right)$.
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CBSE Class 12 Mathematics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.