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

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Solution

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

1 $- \frac{1}{2}$

2 $\frac{1}{2}$

3 $- 2$

4 $2$

Ans.
(4)

Ans. 2

Explanation:

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

$\Rightarrow$ $k = 2$

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