When two lines cross each other, four angles are formed.

An angle is equal to an angle that is opposite to it. In the above image ∠a is opposite (facing) ∠c, so ∠a = ∠c.

∠b is opposite ∠d so

m ∠b = m ∠d

Furthermore, when two lines cross each other, any two angles *next to* each other are supplementary.

## Anonymous

What the m means?

## kiddie

it means measure

## Martana

How do get the numbers for the angles?