# 9.4.2. Main Trigonometrical Ratios of Some Angles

Determine the value of

- A
- B
- C
- D

### Example

Determine the value of

### Solution

Suppose

The cosine of an angle in a right-angled triangle is equal to the
ratio of the length of the adjacent side to the length of the
hypotenuse. The triangle shows that

Thus, the value of the expression