Line L has an undefined slope. Line M is perpendicular to line L. Which of the following could be the equation of line M?

A) x = y
B) y = 7
C) x = -3
D) xy = 4

Can you explain? Thanks!

Respuesta :

"Line L has an undefined slope" so line L is any vertical line. 

Anything perpendicular to this vertical line will be horizontal. So line M is horizontal. 

Horizontal lines are of the form y = k for some fixed number k. The only thing that fits is choice B) y = 7 where k = 7 in this case.

Choice A graphs out a diagonal line, choice C graphs a vertical line, while choice D graphs out a hyperbola. These facts are why we can eliminate these non-answers. 

Answer: Choice B) y = 7