Question

Question #6593b

Answer 1

I will explain it at the "Explanation" section.

Explanation:

Let us have two intersecting lines with angles 1,2,3,4. Look at the picture for help.

We know that `m/_1+m/_2=180`, since they add up to a strait line.

Similarly, we also know that `m/_2+m/_3=180`.

We replace 180 with `m/_2+m/_3` for the first equation to get:
`m/_1+m/_2=m/_2+m/_3` Simplify the equation to get:
`m/_1=m/_3`

Therefore, vertical angles are always congruent.