There is an acute trigonometric function on it.
Find another math textbook for senior one. It has the basic formula of trigonometric function.
First, define the theorem.
Second, commonly used formulas.
Three, three basic function images.
Fourth, use the memory characteristics of images.
Fifth, there are small examples and exercises at the back of each chapter of the textbook. Never ignore it! They are the springboard and bridge to solve difficult problems.
Sixth, if you need to calculate a trigonometric function value in a certain occasion, you can use the calculator on your mobile phone to find it out.
But the trigonometric function values of common angles must be remembered. (30 45 60).
As the saying goes, nothing is difficult in the world.