Question

If the planes $2x-y+\lambda z-5=0$ and $x+4y+2z-7=0$ are perpendicular, then $\lambda =$

• A. $1$
• B. $-1$
• C. $2$
• D. $-2$

Answer 1

Answer: (A)

$1$

Since, the planes $2x-y+\lambda z-5=0$ & $x+4y+2z-7=0$ are perpendicular to each other
Therefore, $(2i-j+\lambda k).(i+4j+2k)=0$
$\Rightarrow 2-4+2\lambda =0$
$\Rightarrow \lambda =1$
Ans: A