Because the knowledge of Pythagorean theorem is proved graphically, the knowledge of quadratic equation and trigonometric function is calculated before and after the square root. This is to combine the knowledge before and after.

In fact, if you look through the math books carefully, you will find that "number", number axis, square number, rational number, irrational number and so on will be involved almost every year in math learning from grade one to grade three. This is a gradual and thorough process. If you learn all the knowledge about "number" or proof in grade one, you will change another knowledge in grade two. Then, with the decline of memory, I can't remember much when reviewing in senior three, so I have to take a little old knowledge with me while learning new knowledge, so that I can take a series of knowledge apart and deepen it.