The equation is .

Let the functions are and .

Draw a coordinate plane.

Graph the function .

Graph the function .

Observe the above two graphs :

The graphs of the two functions coincide.

So, the equation appears to be an identity.

Check algebraically :

The identity is .

Consider right hand side identity : .

Quotient identities :

                                   .

Pythagorean identity : .

=  Left hand side identity.

The equation represents an identity.