Determine the exact value of the following expression by using the difference identity:

sin (315° - 120°)

Express the following sum as one trigonometric function only. Then, determine its exact value by using a unit circle:

sin 68° cos 82° + cos 68° sin 82°

Using a sum or difference formula, determine the exact value of the given trigonometric expression. 

tan(7π/12)

Find the exact value of $\(\sin\]\left\)(x+y\(\right\))$. Use a trigonometric identity.

$\(\cos\) x=\(\frac{5}{11}\)$, $\(\sin\) y=-\(\frac\)18$, $x$ in fourth quadrant, $y$ in third quadrant

Determine the exact value of the following trigonometric function without using a calculator.

$\(\cos\[\left\)(\(\frac{7\pi}{12}\]\right\))$

Determine the exact values of $\(\cos\]\left\)(x+y\(\right\))$ and $\(\cos\]\left\)(x-y\(\right\))$.

$\(\sin\) x=\(\frac{3}{13}\)$, $\(\sin\) y=-\(\frac\)27$, $x$ in quadrant I and $y$ in quadrant III

Which of the following expressions is equivalent to $\(\sin\)78^{\(\circ\)}\(\cos\)34^{\(\circ\)}-\(\cos\)78^{\(\circ\)}\(\sin\)34^{\(\circ\)}$?