$\"\"$

The identity is $\"\"$ .

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

$\"\"$

(Add: $\"\"$ ) \ \

$\"\"$

$\"\"$ (Apply distributive property) \ \

$\"\"$ (Simplify) $\"\"$

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

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

$\"\"$ (Cancel common terms) \ \

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

$\"\"$ is an identity.