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.

$\cos x=\frac{5}{11}$, $\sin y=-\frac18$, $x$ 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 $\cos\left(x-y\right)$.

$\sin x=\frac{3}{13}$, $\sin y=-\frac27$, $x$ in quadrant I and $y$ in quadrant III

Which of the following expressions is equivalent to $\sin78^{\circ}\cos34^{\circ}-\cos78^{\circ}\sin34^{\circ}$?