Trigonometrical Equations
medium

જો $\sec x\cos 5x + 1 = 0$, કે જ્યાં $0 < x < 2\pi $, તો $x =$

A

$\frac{\pi }{5},\frac{\pi }{5}$

B

$\frac{\pi }{5}$

C

$\frac{\pi }{4}$

D

એકપણ નહિ.

(IIT-1963)

Solution

(c) $\sec x\cos 5x = – 1 \Rightarrow \cos 5x = – \cos x$

$ \Rightarrow $ $5x = 2n\pi \pm (\pi – x)$ 

$ \Rightarrow $ $x = \frac{{(2n + 1)\pi }}{6}{\rm{ or }}\frac{{(2n – 1)\pi }}{4}$

Hence $x = \frac{\pi }{4},\,\frac{\pi }{2},\,\frac{{3\pi }}{4},\,\frac{{5\pi }}{6},\,\frac{{5\pi }}{4},\,\frac{{7\pi }}{6},\,\frac{{7\pi }}{4},\,\frac{{9\pi }}{6},\,\frac{{11\pi }}{6}$.

Standard 11
Mathematics

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