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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