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 Click on this button below to see the correct answer 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 Click this button to see if you are correct 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 Click on this button to see the correct answer to see the answer.

Question 1
All of the angles in the diagram below are equal to either angle g or angle h.
 
For each angle below, say which angle it is equal to:

Angle a is equal to
Angle b is equal to
Angle c is equal to
Angle d is equal to
Angle e is equal to
Angle f is equal to

Question 2
Find the size of each of the angles marked with letters in the diagrams below:
(a)

 

 a = °    
b = °    
(b)

 

 a = °    
b = °    
c = °    
(c)

 

 a = °    
b = °    
c = °    
d = °    
(d)

 

 a = °    
b = °    
c = °    
d = °    
Question 3
Find the size of each of the angles marked with letters in the diagram below:
a = °    
b = °    
c = °    
d = °    
e = °    
Question 4
Find the size of each of the angles marked with letters in the diagram below:
a = °    
b = °    
c = °    

What special name is given to the triangle in the diagram?

Question 5
Find the size of each of the angles marked with letters in the diagram below:
a = °    
b = °    
c = °    
Question 6
The diagram shows a triangle on top of a trapezium.
Find the size of each of the angles marked with letters in the diagram below:
a = °    
b = °    
c = °    
d = °    

You have now completed Unit 11 Section 2
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Produced by A.J.Reynolds August 2007