(2)sin2a=4/5, cos2a=3/5, and the original formula =-1/2 (COS2A-SIN2A)+5/2 =13/5.

2. Generally, the period of a function is to draw the analytic expression, and that's all.

The maximum value depends on the increase or decrease of independent variables and the scope of the definition domain, and is generally calculated by combining numbers and shapes.

Some problems will involve quadratic function, that is, we need the knowledge of quadratic function to find the maximum value. Generally, we should pay attention to these: the axis of symmetry, the range of independent variables, the direction of opening, monotonicity, and then combine the characteristics of trigonometric functions to solve them. Mainly based on specific problems, it is relatively easy to say.

The general method of finding the maximum value can also be used universally.

As for the first question, like that type of question, that is, the evaluation question, if you can simplify it, make full use of the conditions in the question and draw the implied conclusion you want, then how to calculate it is a question of using the formula flexibly, and I can only stop here.

Personally, trigonometric function belongs to the simplest knowledge plate in high school mathematics. As long as you can skillfully and flexibly apply the formula, you sometimes need to use the ideas of combination of numbers and shapes, classification discussion, equivalent transformation and so on. I suggest you remember the conclusive things, which will speed up the speed and quality of solving problems.

If you don't understand anything, you can send me a message and be happy to answer.

I am a big fan of mathematics.

The above is only a personal opinion, I hope it will be useful to you.