Unit 11 Section 2 : Parallel And Intersecting Lines
When a line intersects (or crosses) a pair of parallel lines, there are some simple rules that can be used to calculate unknown angles.
The arrows on the lines indicate that they are parallel.

 
A simple way to remember this is that any pair of angles will be equal or they will add up to 180°.
Usually you can work out which is correct by looking at the diagram.

Practice Questions
Work out the answer to each of these questions then click on the button marked
to see whether you are correct.
Practice Question 1
In the diagram below, the angle a = 150°.

Find the size of the unknown angles:
b =
c =
d =
e =
Note that there will often be more than one way of finding each angle.

Practice Question 2
The diagram below shows a parallelogram  the opposite sides are parallel lines.

Find the size of the unknown angles:
HINT: If you click on the parallelogram, the parallel lines will be extended at the corners to help you.
a =
b =
c =

Exercises
Work out the answers to the questions below and fill in the boxes. Click on the
button to find out whether you have answered correctly. If you are right
then will appear and you should move on to the next
question. If appears then your answer is wrong. Click
on to clear your original answer and have another go.
If you can't work out the right answer then click on
to see
the answer.
You have now completed Unit 11 Section 2
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