**What is Trigonometry?**

Trigonometry is a branch of mathematics which deals with the relation between different angles and sides of a triangle. Basically trigonometry deals with a right triangle. Different
trigonometric ratios are defined with respect to the two acute angles in the **right triangle**. Consider the right triangle ABC given below with angle B as right angle.

We can define trigonometric ratio taking any of the angles A and C into consideration. Let us first try to define these ratios, taking angle C as θ. The most important thing to note down is that:

Side opposite to right angle is called **hypotenuse (H)**

Side opposite to the acute angle in consideration (θ) is called **perpendicular (P)**

Side adjacent to the acute angle in consideration (θ) is called **base (B)**

Here in the given triangle AC is hypotenuse, AB is altitude and BC is base.

Now, you might have a clear picture of all three sides a triangle. Let us now try to understand different trigonometric ratios.

**Sine Ratio:** Abbreviated as ** sin,** is defined as the ratio of perpendicular to hypotenuse.

**Cosine Ratio:** Abbreviated as ** cos**, is defined as the ratio of base to hypotenuse.

**Tangent Ratio:** Abbreviated as ** tan**, is defined as the ratio of perpendicular to base.

So we conclude that sine ratio involves the opposite and hypotenuse whereas cosine ratio involves the adjacent and hypotenuse. Tangent ratio involves the opposite and adjacent sides of the triangle.

**1.** Name the opposite and adjacent sides for θ in the triangle shown below.

**Solution:**

The opposite side is PQ and adjacent side is QR.

2. Define trigonometric ratios for angle R in triangle shown below.

**Solution:**

The trigonometric ratios are: