Practicing Success
If a line makes angles $\frac{2\pi}{3}$ and $\frac{\pi}{3}$ with positive direction of x-axis any y-axis respectively, then the acute angle made by the line with positive z-axis is : |
$\frac{\pi}{3}$ $\frac{\pi}{4}$ $\frac{\pi}{6}$ $\frac{\pi}{2}$ |
$\frac{\pi}{4}$ |
The correct answer is Option (2) → $\frac{\pi}{4}$ let angles made with $x, y, z$ be $α,β,γ$ $\cos^α+\cos^2β+\cos^2γ=1$ so $\cos^2\frac{2π}{3}+\cos^2\frac{π}{3}+\cos^2γ=1$ $\frac{1}{4}+\frac{1}{4}+\cos^2γ=1$ so $\cos^2γ=\frac{1}{2}⇒\cos γ=\frac{1}{\sqrt{2}}$ $γ$ is acute so $γ=\frac{\pi}{4}$ |