These are my guidelines for solving such equations. Usually the range given is 0 deg < x < 360 deg or 0 rad < x < 2pi rad (sometimes given as <=, less than or equal to).

If the angles given are different, for example, 2x or (3x + 15 deg) instead of x, or if the range given is different, for example, 0 deg < x < 720 deg, then other additional steps are required prior to Step 1.

Fortunately, as an introduction to you for solving such questions for the first time, all the parts in Question 9 are given as angle x, so that you can get used to how to solve such questions before the question gets extended to include a wider range of angles or to include weird angles.

Here are my workings for Q9a based on my guidelines to solve such trigonometric equations.

I may not be completing every question in this session since it is getting late at this hour.

You will need to master the techniques to solve these equations as these will become important as you attempt to solve more difficult and more complex trigonometric equations.

Parts (b), (c) and (d)

Parts (e) and (f)

Let me know if you need more explanations or do not understand my workings.