see the INDEX of all topics here or go to the relevant topics below
Remember only two things: 1) if the side is next to the angle, use Cos and 2) if the side is opposite to the angle, use Sin.
That’s all you need to remember. And don’t forget to multiply with the hypotenuse. [We have used different alphabets for denoting the hypotenuse. Get used to that. Know that an alphabet is just a placeholder for a number. When you see a or k or t or m in these diagrams, assume that they are some number like 5, 7, 27, 33. Initially this will make it easier for you to understand. Later you will get very used to it.]