The sine of an angle is defined using a right triangle. When we have a right triangle, the sine is equal to the length of the side opposite the angle divided by the length of the hypotenuse of the triangle. Sine is abbreviated by “sin”. In this-sub-topic, we will learn about sine of an angle and the sine rule.

Recall that solving a triangle involves finding the lengths of all sides and the measures of all angles in the triangle. In a right-angled triangle, the sine of an angle is the length of the side opposite the angle divided by the length of the hypotenuse. Sine of an angle is used to solve a right triangle.

△ABC is right triangle. So, the side BC is the side opposite to angle θ and the side AB is the hypotenuse of right △ABC. In solving a right triangle, we use sine ratio formula:

The circle with center (0, 0) and radius 1 unit is called the unit circle.