Question

If the planes $x + 2y + kz = 0$ and $2x + y - 2z = 0$ are at right angles, then the value of k is

• A. $- \frac{1}{2}$
• B. $\frac{1}{2}$
• C. – 2
• D. 2

Answer 1

Answer: (D)

2

Answer 2

Obviously, $2 ( 1 ) + 1 ( 2 ) - 2 ( k ) = 0 \Rightarrow k = 2$ .