Question Detail
Question
Find the angle between A = (i + 2j - k) and B = (-i + j - 2k).
Correct Answer
Option A is the correct answer.
Detailed Explanation
A·B = (1)(-1) + (2)(1) + (-1)(-2) = -1 + 2 + 2 = 3. |A| = √(1²+2²+(-1)²) = √(1+4+1)=√6. |B| = √((-1)²+1²+(-2)²) = √(1+1+4)=√6. cos θ = 3/(√6×√6) = 3/6 = 0.5. So θ = 60°.
Hint
Use dot product formula: A·B = |A||B| cos θ.