This series of methods often give some conditions, such as a greater than or equal to 0 and less than or equal to 1. B is greater than or equal to 1, less than or equal to these given some special conditions, and then let you find the combination of ab, it may be very complicated. But if it is a multiple-choice question, you can try a=0.5 and b= 1.5. There is also a formula that can bring the answers in the options to the questions for calculation.

2. Interval method

This method, also called exclusion method, relies on roughly calculated data or guesses some data. For example, how many angles are given to a topic, 30 and 90. Obviously, the answer must be 90 30 degrees, 120 plus or minus 30 degrees. Or some answers related to 30, 60 or 90 degrees.

3. Coordinate method

If you can't find ideas on some graphic problems, you can use the proportional method first, and then use the coordinate method. You can directly find the coordinates of two points without any trigonometric function, and directly bring in the high school function to find the angle (cos formula), vertical line, length and tangent separation formula.