Year 9

Year 9

# Using inverse sine and cosine to find missing angles

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## Lesson details

### Key learning points

1. In this lesson, we will use inverse sine and cosine to find missing angles in triangles.

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This content is made available by Oak National Academy Limited and its partners and licensed under Oak’s terms & conditions (Collection 1), except where otherwise stated.

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## Worksheet

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## Starter quiz

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### 7 Questions

Q1.
What is the length of side marked q ?
10 cm
Correct answer: 2.5 cm
5 cm
Q2.
What is the length of the side marked r ?
15 cm
22 cm
Correct answer: 5.5 cm
Q3.
What is the correct step for calculating the length of side b?
Correct answer: Option 1
Option 2
Option 3
Q4.
What is the length of of b correct to 1 decimal place?
0.86 cm
10 cm
Correct answer: 10.6 cm
Q5.
What is the correct step for calculating the length of side a?
Option 1
Option 2
Correct answer: Option 3
Q6.
What is the length of a, correct to 1 decimal place?
0.5 cm
23 cm
Correct answer: 23.0 cm
39.2 cm
Q7.
Which ratio would you use to find the length of the missing side in the triangle below?
Correct answer: cosine
pythagoras
sine

## Exit quiz

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### 6 Questions

Q1.
Fill in the gap: You can use the inverse sine function to work out the unknown angle, when given the opposite and ................. in a right- angled triangle.
adjacent
Correct answer: hypotenuse
symmetry
Q2.
Fill in the gap: You can use the inverse cosine function to work out the unknown angle, when given the hypotenuse and ................. in a right- angled triangle.
Correct answer: adjacent
opposite
symmetry
Q3.
Use the sine ratio to find out the missing angle in the triangle shown below.
15 degrees
Correct answer: 30 degrees
45 degrees
60 degrees
Q4.
Which is the correct method to work out the missing angle?
Correct answer: Cosine
Pythagoras
Sine
Q5.
Which is the correct method to work out the missing angle?
Cosine
Pythagoras
Correct answer: Sine
Q6.
Which is the correct method to work out the length of missing side?
Correct answer: Cosine
Pythagoras
Sine