A line makes the same angle $\theta$, with each of the $x$ and $z$ axis. If the angle $\beta$, which it…

A line makes the same angle $\theta$, with each of the $x$ and $z$ axis. If the angle $\beta$, which it makes with $y$-axis, is such that $\sin ^2 \beta=3 \sin ^2 \theta$, then $\cos ^2 \theta$ equals
  1. $\frac{2}{3}$
  2. $\frac{1}{5}$
  3. $\frac{3}{5}$
  4. $\frac{2}{5}$

Solution

$I=\cos \theta, m=\cos \theta, n=\cos \beta$ $\cos ^2 \theta+\cos ^2 \theta+\cos ^2 \beta=1 \Rightarrow 2 \cos ^2 \theta=\sin ^2 \beta=3 \sin ^2 \theta \quad$ (given) $\cos ^2 \theta=3 / 5$

Asked in: JEE Main 2004

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