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 48S2π2 is ____.

Solution

S2=π83π8sin2x4x-πdx   i

S2=π83π8sin23π8+π8-x43π8+π8-x-πdx

S2=π83π8cos2xπ-4xdx    ii

From (i) and (ii), we get

2S2=π83π84x-πdx

2 S2=π216

S2=π232

48S2π2=4832

48S2π2=32=1.5

Asked in: JEE Advanced 2021 (Paper 2)

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