2: It’s either sine, cosine, or tangent.
4: Three of these are all the same value.
6: The sine of one angle is the cosine of the other angle.
9: It’s best if you simplify, but not required in this case.
12: See #6.
21: Start with sin 71° or cos 71°, because you know the length of the hypotenuse and sine and cosine both use the hypotenuse.
23: After setting up the initial equation, multiply both sides by the denominator, whether it is a number or a variable.
26: Two of the ratios are 2 over 4.
27: Try each possibility, and simplify to see if equals √3/2.
30: Change the function, or change the ratio.
31: Set up sine, cosine, or tangent equation with one variable, and multiply each side by the denominator.
48: Both are correct (explain why).
53: To divide by a fraction, multiply by its reciprocal.