Using the cosine ratio
I can use the cosine ratio to find the missing side or angle in a right-angled triangle.
Using the cosine ratio
I can use the cosine ratio to find the missing side or angle in a right-angled triangle.
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Lesson details
Key learning points
- The cosine ratio involves the hypotenuse, adjacent and the angle.
- If you know the length of the hypotenuse and the size of the angle, you can use the cosine ratio.
- If you know the length of the adjacent and the size of the angle, you can use the cosine ratio.
- If you know the length of the hypotenuse and adjacent, you can use the cosine ratio.
Keywords
Hypotenuse - The hypotenuse is the side of a right-angled triangle which is opposite the right angle.
Adjacent - The adjacent side of a right-angled triangle is the side which is next to both the right angle and the marked angle.
Trigonometric functions - Trigonometric functions are commonly defined as ratios of two sides of a right-angled triangle containing the angle.
Cosine function - The cosine of an angle (cos(θ°)) is the x-coordinate of point P on the triangle formed inside the unit circle.
Common misconception
The cosine formula is only used to find the length of a side adjacent to an angle.
The cosine formula can be used to find the length of a side adjacent to an angle. A rearrangement of the formula also allows us to find the length of the hypotenuse given the adjacent side. The arccosine function allows us to find the angle, itself.
Licence
This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).
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Starter quiz
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