Question

The equation $xy=0$ in three dimensional space represents

• A. a pair of straight lines
• B. a plane
• C. a pair of planes at right angles
• D. a pair of parallel planes.

Answer 1

Answer: (C)

$xy=0$ $\iff$ $x=0$ or $y=0$. Hence, locus of $xy=0$ is the union of all points which lie in $YOZ$ plane or on $ZOX$ plane. So the equation $xy=0$ represents a pair of perpendicular planes