Q216 / 270 · NDA 2012 (Phase 1) · Mathematics

What is the cosine of angle between the planes $x+y$ $+z+1=0$ and $2 x-2 y+2 z+1=0$ ?

  • A
    1/2
  • Correct answer
    B
    1/3
  • C
    2/3
  • D
    None of the above

Solution

$\cos \theta=\frac{1(2)+1(-2)+1(2)}{\sqrt{1^2+1^2+1^2} \cdot \sqrt{2^2+(-2)^2+2^2}}=\frac{2}{\sqrt{3} 2 \sqrt{3}}=\frac{1}{3}$.

Hence, the correct answer is option: 'B'.

Relevant Questions