12. Trigonometric Identities

Find the exact value of the expression.

$\(\cos\)105\(\degree\)$

Find the exact value of the expression.

$\(\sin\)15\(\degree\)$

Find the exact value of the expression.

$\(\cos\]\frac{5\pi}{12}\)$

Find the exact value of the expression.

$\(\cos\)80\(\degree\[\cos\)20\(\degree\)+\(\sin\)80\(\degree\]\sin\)20\(\degree\)$