Skip to main contentSkip to solution

If a⃗,b⃗,c⃗\vec a, \vec b, \vec c are mutually perpendicular vectors of equal magnitude, the angle between a⃗+b⃗+c⃗\vec a+\vec b+\vec c and a⃗\vec a is

Solution

✅ Correct Option: 3

Let each magnitude be kk. Since the dot products vanish pairwise, ∣a⃗+b⃗+c⃗∣=3k|\vec a+\vec b+\vec c|=\sqrt{3}k and (a⃗+b⃗+c⃗)⋅a⃗=k2(\vec a+\vec b+\vec c)\cdot\vec a=k^2.

So cos⁡θ=k23k⋅k=13\cos\theta=\frac{k^2}{\sqrt{3}k\cdot k}=\frac{1}{\sqrt3}.

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question