Angles Edexcel International GCSE Mathematics A revision
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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.
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?
A straight line is half a full turn.
Two angles of a triangle are 50° and 60°. What is the third?
180 − 110.
Which angles between parallel lines are equal and make a Z shape?
They are on opposite sides of the line that crosses.
What do the angles in a quadrilateral add up to?
It can be cut into two triangles.
Two straight lines cross. One of the angles is 35°. What is the angle opposite it?
Vertically opposite angles are equal.
Quiz
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
Edexcel International GCSE Mathematics A 4MA1 · 6 marks · papermunch.org
Name ______________________________ Date ______________
Two angles of a triangle are 47° and 68°. Find the third angle.[2]
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65°. 180 − 115.
Three angles round a point are 110°, 95° and x. Find x.[2]
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155°. 360 − 205.
An isosceles triangle has one angle of 40° between its two equal sides. Find the other two angles.[2]
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70° each. (180 − 40) ÷ 2.
Answers: Angles
- 1. 65°. 180 − 115.
- 2. 155°. 360 − 205.
- 3. 70° each. (180 − 40) ÷ 2.