Replicon is totally right. The way to learn maths is to understand it, which is also the case with most of science. This has many advantages: firstly, you can pretty much never forget something if you understand why it is true. Secondly, you will be a lot more confident with applying your knowledge, especially to novel situations. Thirdly, it's a lot easier to learn more stuff which builds on this knowledge, and the thing about maths is that new stuff always builds on what came before.

The only things you need to learn are definitions, and the number of these is tiny. In the case of trig, there are three main definitions;



cos(A) is the length of the adjacent (the side touching A) divided by the hypotenuse, sin(A) is similar but is the opposite side divided by the hypotenuse, and finally tan(A) is the opposite side of A divided by the adjacent side.

Already you can deduce one formula: tan(A) = sin(A)/cos(A)

This is because by definition sin(A)/cos(A) is

(opposite/hypotenuse) / (adjacent/hypotenuse),

and then by the basic laws of fractions you just cancel the /hypotenuse on the top and the bottom to find that it

= opposite/adjacent,

which is tan(A) by definition.

This is a perfect example; by understanding the above formula, that it is a simple consequence of cancelling the hypotenuses, you will never forget it; you understand that it is obviously true. However, somebody who doesn't put in the half a minute required to understand it instead has to memorise the entire formula, which ultimately will take much longer, much more effort, and they will have no means of knowing if what they've put is actually right.