Year 9

# Using inverse sine and cosine to find missing angles

Year 9

# Using inverse sine and cosine to find missing angles

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## Lesson details

### Key learning points

- 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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### 7 Questions

Q1.

What is the length of side marked q ?

10 cm

5 cm

Q2.

What is the length of the side marked r ?

15 cm

22 cm

Q3.

What is the correct step for calculating the length of side b?

Option 2

Option 3

Q4.

What is the length of of b correct to 1 decimal place?

0.86 cm

10 cm

Q5.

What is the correct step for calculating the length of side a?

Option 1

Option 2

Q6.

What is the length of a, correct to 1 decimal place?

0.5 cm

23 cm

39.2 cm

Q7.

Which ratio would you use to find the length of the missing side in the triangle below?

pythagoras

sine

### 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

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.

opposite

symmetry

Q3.

Use the sine ratio to find out the missing angle in the triangle shown below.

15 degrees

45 degrees

60 degrees

Q4.

Which is the correct method to work out the missing angle?

Pythagoras

Sine

Q5.

Which is the correct method to work out the missing angle?

Cosine

Pythagoras

Q6.

Which is the correct method to work out the length of missing side?

Pythagoras

Sine