Ratios and Graphs of Trigonometric Functions
Cosine
A trigonometric ratio; for a right-angled triangle, adjacent over hypotenuse, extended to any angle.
| English | Cosine |
|---|---|
| Bahasa Melayu | Kosinus |
| 中文 | 余弦 |
How it is used
In a right-angled triangle the side adjacent to a 60° angle is 6 cm and the hypotenuse is 12 cm, so cos 60° = 6/12 = 0.5, which agrees with the special-angle value.
Where it shows up in SPM
Cosine appears in the Trigonometric Ratios chapter of Form 4 and 5. In Paper 2 it links the adjacent side and hypotenuse when finding a missing length or angle, and in Paper 1 you state cos θ for special angles or its sign in a given quadrant.
Don't confuse it with
Open the chapter: Ratios and Graphs of Trigonometric Functions →
Frequently asked questions
Why is cos θ negative in the second quadrant?
In the second quadrant the x-coordinate on the unit circle is negative, and cosine matches that x-value. So cos 120° = −cos 60° = −0.5.
The quadrant sign rule (only sine is positive in the second quadrant) confirms this.
What is the connection between sin θ and cos θ?
For any angle, sin²θ + cos²θ = 1, so if you know one you can find the other. Also cos θ = sin(90° − θ); for example cos 40° = sin 50°.
These links let you check answers and convert between the two ratios.