Step by step
The question
Question: find out if the two lines are parallel.
The corresponding angles are 5x and 4x + 12, with x = 15.
1 Put x in
Put x = 15 in the angle 5x.
That is 75°.
Put x = 15 in the angle 4x + 12.
That is 72°.
2 Name the angle pair
A line crosses two other lines.
It is called a transversal.
Our two angles are in the same place at each crossing: corresponding angles.
Together they make an F shape.
3 Use the parallel test
If the lines are parallel, both crossings look the same, so corresponding angles are equal.
And if they are equal, the lines are parallel.
75° and 72° are not equal.
Careful!
For corresponding angles we ask: are they equal?
So the lines are not parallel.
If we carry the lines on, they would meet.
Look at the picture: the top line is turned.
Let's look back.
First: put x in.
Then: name the angle pair.
Last: use the parallel test.