Are you going to ask how to do the corner intersection problem? You need to use three theorems, sine theorem, cosine theorem and triangle area formula to do it.

There are four techniques for corner swap: 1. When there are fractions, equations or inequalities about angles in the topic, this formula is generally a relational expression, not a specific value, so it is necessary to consider whether it is suitable for angle and angle exchange;

2. The principle of corner interaction is: simplify the complex and turn the unknown into the known;

3. More often, the sine theorem is used for simplification, especially when there is a homogeneous formula. When there is a formula related to the cosine theorem, such as Example 3 above, the cosine theorem will be used;

4. If the coordinates of the formula are all sides and the cosine value is on the right, the formula on the left is obviously not a cosine theorem, and the cosine value on the right will generally become an angle.