**1. Trigonometry:**

In a right angled OAB, where BOA = ,

**2. Trigonometrical Identities:**

**3. Values of T-ratios**

**4. Angle of Elevation:**

Suppose a man from a point O looks up at an object P, placed above the level of his eye. Then, the angle which the line of sight makes with the horizontal through O, is called the **angle of elevation** of P as seen from O.

Angle of elevation of P from O = AOP.

**5. Angle of Depression:**

Suppose a man from a point O looks down at an object P, placed below the level of his eye, then the angle which the line of sight makes with the horizontal through O, is called the **angle of depression** of P as seen from O.