Simplification: Generally speaking, what is the analytic formula f(x)= of a function? We must simplify it and seek maximum monotonicity or something.

Evaluation: Generally, simplify it first, or transform the known and the unknown, so we must make full use of the known conditions. Basically, the formula is reversed. First, we should pay attention to the range of angles.

Proof: Prove from left to right, prove from right to left, both sides can be in the middle, and try to make the parts on both sides the same.

Suggestion: if you can square it, use less square to avoid analyzing the pros and cons after opening up.

The formula a * b = absin (r) for multiplying vector angle and vector coordinates is the most commonly used vector word. You should have learned it, and the representation of vectors.

Then it is suggested that some geometric problems (mainly proof problems) should be expressed by bases, and if they are vertical, they should be expressed by coordinates.