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Start with the given expression.

Use the identity

to expand the expression.

Using the unit circle, evaluate

to get

and evaluate

to get

Multiply

Combine the fractions.

Multiply the first fraction by the reciprocal of the second fraction.

Cancel out the common terms.

Simplify.

Multiply the fraction by

Combine the fractions.

FOIL

Combine like terms

Factor out the GCF

Reduce
So