Let $g_{i}:\left[\frac{\pi}{8}, \frac{3 \pi}{8}\right] \rightarrow \mathbb{R}, i=1,2$, and…

Let $g_{i}:\left[\frac{\pi}{8}, \frac{3 \pi}{8}\right] \rightarrow \mathbb{R}, i=1,2$, and $f:\left[\frac{\pi}{8}, \frac{3 \pi}{8}\right] \rightarrow \mathbb{R}$ be functions such that $g_{1}(x)=1, g_{2}(x)=|4 x-\pi|$ and $f(x)=\sin ^{2} x$, for all $x \in\left[\frac{\pi}{8}, \frac{3 \pi}{8}\right]$ Define $$ S_{i}=\int_{\frac{\pi}{8}}^{\frac{3 \pi}{8}} f(x) \cdot g_{i}(x) d x, \quad i=1,2 $$ The value of 16S1π is ___.

Solution

S1=π83π8sin2x·1dx    ...i

S1=π83π8sin23π8+π8-xdx

S1=π83π8cos2xdx   ..ii

From (i) and (ii), we get

2S1=π83π81dx

2S1=π4

16 S1π=2

Asked in: JEE Advanced 2021 (Paper 2)

Practice more Definite Integration questions on Aicharya