Question

Write a paragraph proof of this theorem: In a plane, if two lines are perpendicular to the same line, then they are parallel to each other.

Given: R ] S, T ] S
Prove: R II T

Answer 1

If you call the gradient of S m:

Gradient of R if perpendicular to S = -1/m

Gradient of T if perpendicular to S = -1/m

-1/m=-1/m, so the lines are parallel