$\"\"$

The identity is $\"\"$

To take the left hand side expression for prove that right hand side expression.

$\"\"$

(Multiply numerator and denominator by $\"\"$ ) \ \

$\"\"$

$\"\"$ (Apply formula: $\"\"$ )

(Apply Pythagorean identity: $\"\"$ ) \ \

$\"\"$ $\"\"$

$\"\"$ (Multiply numerator) \ \

(Divide: $\"\"$ )

$\"\"$

$\"\"$ (Write complete square) \ \ $\"\"$

$\"\"$ is an identity. \ \