Trigonometry

Right Angled Triangles |  Trigonometric Ratios |  Special Angles  |  Inverse Trigonometric Functions  |  Finding the Length of a Side of a Triangle  |  Trigonometric Identities  |  Miscellaneous  

Trigonometric Identities

If the hypotenuse of a right angled triangle is 1 unit, then by the definitions of the sine and the cosine the opposite side is sin θ and the adjacent side is cos θ.

By the Pythagoras Theorem,

This is usually written as 

Dividing the above identity by cos²θ, we get

Divide the identity by sin ²θ, we get

The three formulas given in the boxes above are known as trigonometric identities as they provide relationships between trig functions. These identities are useful in solving a variety of problems. There are more trig identities that are not as easy to establish: More Trig Identities

Next - Miscellaneous

Right Angled Triangles |  Trigonometric Ratios |  Special Angles  |  Inverse Trigonometric Functions  |  Finding the Length of a Side of a Triangle  |  Trigonometric Identities  |  Miscellaneous