To define Trigonometric function, consider a right triangle XYZ with angle $\theta $ as shown in the figure above.

**If $\theta $ is taken as an angle of reference,**

1) **YZ** the side opposite to $\theta $ is called the perpendicular, in this case side "**a**".

2) **XY** the side opposite to the right angle is called the hypotenuse, in this case side "**h**".

Hypotenuse is always the longest side of a right-angled triangle.

3) **XZ** the third side is called the base, in this case side "**b**".**The Trigonometric Functions are:** **Pythagoras' Theorem:**In a right angled triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides.

** **
**$a^{2} + b^{2} = c^{2}$**