We will work with just the left side:

Use the quotient identity 
to rewrite the first term:




Multiply the second fraction by 
which just equals 1:


 

Multiply the fractions:



Use the Pythagorean identity  written as 
to replace the second denominator:



Simplify the second term on the bottom:





The denominators are the same so we can combine the
two fractions by combining the numerators over the
common denominator:



Simplify the numerator:





Use the reciprocal identity 



Edwin