- Home
- Std 11
- Mathematics
4-1.Complex numbers
easy
यदि $x + \frac{1}{x} = 2\cos \theta $, तो $x$ का मान होगा
A
$\cos \theta + i\,\sin \theta $
B
$\cos \theta - i\,\sin \theta $
C
$\cos \theta \pm i\,\sin \theta $
D
$\sin \theta \pm i\,\cos \theta $
Solution
(c) $x + \frac{1}{x} = 2\cos \theta $$ \Rightarrow \,{x^2} – 2x\cos \theta + 1 = 0$
==> $x = \frac{{2\cos \theta \pm \sqrt {4{{\cos }^2}\theta – 4} }}{2}$
==> $x = \cos \theta \pm i\sin \theta $.
Std 11
Mathematics
