It is asking you to use the information to find the sizes of angles a and b.
Let's practise
Thomas draws a triangle.
The largest angle a is double the size of the smallest angle b.
Angle c is 30°.
Find the sizes of angles a and b.
a =°
b =°
- Read the question and then read it again. What is it asking you to do?
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- What angle sizes do you already know?
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One of the angles is 30°.
- What do you know about the sum of angles in a triangle?
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Angles in a triangle add up to 180°.
- Subtract the size of the angle you know from 180°. This gives you the total of angles a and b.
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180° – 30° = 150°
So, angles a + b = 150°.
- What else do you know about angles a and b?
It may be useful to write a list of pairs of angles that sum to 150° and look for a pair that matches the information you are given.
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Angle a is double the size of angle b.
140° + 10° = 150°
130° + 20° = 150°
120° + 30° = 150°
110° + 40° = 150°
100° + 50° = 150°
100° is double 50°.
- What is your answer?
Check your working.
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a = 100° and b = 50°.
You can check that the angles sum to 180°:
100° + 50° + 30° = 180°