Trigonometric functions are functions, and quadrant symbols are labeled. Function image unit circle, periodic parity increase and decrease. Any function of a vertex is equal to the division of the last two. The latter is regarded as an acute angle, and the sign is judged as the original function.

The cosine of the sum of two angles is converted into a single angle, which is easy to evaluate. Calculation proves that the angle is the first. Pay attention to the name of the structural function, cosine plus cosine, cosine minus sine, trigonometric function is the inverse function. The essence is to find the angle, first find the trigonometric function value, and then judge the range of the angle. Using right triangle, the image is intuitive and easy to rename. The equation of a simple triangle is reduced to the simplest solution set.

Learning skills:

First of all, make clear the meaning of the question and see if there are any special requirements such as simple method and keeping several decimal places; Secondly, observe the characteristics of the topic and see if there are several simple algorithms for operation; Third, determine the operation sequence. On this basis, relevant rules and laws are adopted for calculation; Finally, carefully check whether there are any mistakes, omissions or miscalculations.

To solve the problem model, the first step is to observe whether the known and the unknown are at the same angle. If they are the same, use the basic relationship of the same angle to solve them. If they are different, proceed to the second step. The second step is to observe whether the known and unknown are at the same angle. If they are the same, find the sum and difference of the two angles as the special value, and use the known angle to indicate that the unknown keratinization is the same angle problem. Step 1, if not, continue to step 3.

The third step, because the known and the unknown are not at the same angle. Therefore, the low magnification angle can be equally divided and then the multiple of the second elevation angle can be reduced, or the high magnification angle can be enlarged and then the multiple of the angle can be reduced, and then the second step can be carried out.