What do the angles on a straight line add up to?

180°. A straight line is half a full turn.

Which angles between parallel lines are equal and make a Z shape?

alternate angles. They are on opposite sides of the line that crosses.

What do the angles in a quadrilateral add up to?

360°. It can be cut into two triangles.

Two straight lines cross. One of the angles is 35°. What is the angle opposite it?

35°. Vertically opposite angles are equal.

Angles · Cambridge IGCSE Mathematics (9

In plain words

Angle questions look like puzzles, but there are only a handful of rules. Find one that fits, work out an angle, and that usually unlocks the next one.

Three things to know

Angles on a straight line add up to 180°. Angles round a point add up to 360°. Vertically opposite angles are equal.
The angles in a triangle add up to 180°, and in a quadrilateral to 360°. An isosceles triangle has two equal angles.
With parallel lines: alternate angles are equal (a Z shape), corresponding angles are equal (an F shape), and co-interior angles add up to 180° (a C shape).

Worked example

The angles of a triangle are x, 2x and 3x. Find x.

The angles add up to 180°: x + 2x + 3x = 180.
6x = 180.
x = 30°.

Tips and tricks

Give the reason in words when asked: "alternate angles are equal", not "Z angles".
Write each angle on the diagram as you find it.

5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Angles: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What do the angles on a straight line add up to?
- 90°
- 180° (the answer)
- 270°
- 360°
A straight line is half a full turn.
Two angles of a triangle are 50° and 60°. What is the third?
- 60°
- 70° (the answer)
- 80°
- 110°
180 − 110.
Which angles between parallel lines are equal and make a Z shape?
- alternate angles (the answer)
- corresponding angles
- co-interior angles
- vertically opposite angles
They are on opposite sides of the line that crosses.
What do the angles in a quadrilateral add up to?
- 180°
- 270°
- 360° (the answer)
- 540°
It can be cut into two triangles.
Two straight lines cross. One of the angles is 35°. What is the angle opposite it?
- 35° (the answer)
- 55°
- 145°
- 325°
Vertically opposite angles are equal.

5 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

3 questions, 6 marks. Write your answers on paper, then check them.

Angles

Cambridge IGCSE Mathematics (9–1) 0980 · 6 marks · papermunch.org

Name ______________________________ Date ______________

Two angles of a triangle are 47° and 68°. Find the third angle.[2]
Show answerHide answer
65°. 180 − 115.
I got this one
Three angles round a point are 110°, 95° and x. Find x.[2]
Show answerHide answer
155°. 360 − 205.
I got this one
An isosceles triangle has one angle of 40° between its two equal sides. Find the other two angles.[2]
Show answerHide answer
70° each. (180 − 40) ÷ 2.
I got this one

Answers: Angles

1. 65°. 180 − 115.
2. 155°. 360 − 205.
3. 70° each. (180 − 40) ÷ 2.