Finite and infinite means that when you do limit problems, you can find the law through a limited range. In fact, sometimes you can introduce some special values. Possibility necessarily refers to the transformation between quantifiers in logical reasoning. If you find it difficult to do the problem, you can turn it into a negative proposition to judge whether it is true or not. In reasoning, analogical reasoning is from special to general, and the college entrance examination often takes blank questions. At this time, you should pay attention to check whether the result of analogy is correct.

Separating variables is useful for evaluating fields, but it cannot be generalized. Try it when you see the second score, but don't just memorize it. Sometimes it's not easy. At the end of the interval, we must pay attention to whether we can get it or not, and pay attention to the domain and monotonicity of the function.

Trigonometric function means that it is best to change the solution to the same degree, which can be simplified, and it is best to change it to the same side or angle. If they are all angles, pay attention to the Hua Song string or Hua Song cut.

Parameter uncertainty means that the range can be judged by parameter equation. Monotonicity, parity, method of substitution and so on can be used if the left and right forms are different.

The minimum distance between two points on a sphere refers to the lower arc length of the great circle passing through the center of the sphere and the two points.