Hello.
First, draw a picture of two parallel lines and a transversal.
Find the two same side angles, either the same side interior or the same side exterior.
We do not know the measurement of the angle, so we'll label it x.
The second angle is 20° smaller than the other one so we'll label is x-20
Same side angles are supplementary. Meaning that they add up to 180°
Next, make an equation.
1st angle + 2nd angle = 180°
Now substitute the first and second angle to x and x-20
The substituted equation should now look like this.
x+x-20=180
solve it and you'll get...
x=100
But we're not done.
The angle labeled x is 100°
The other one is x-20
And since x=100, the second angle is 100-20=80°
Now use linear pairs, more same side angles, vertical angles, alternate angles, and linear pairs, to label the rest. Remember that each angle is either 100° or 80°.
Hope this helped!
-Emily
