The circle is one of the simplest geometric figures, which can be drawn with only one stroke. But learning a circle is not as simple as its shape. To learn a circle, we should not only understand its concept, but also master the relevant calculation formulas (arc length, sector area, etc.). ), positional relationship, properties and related theorems.

The main purpose of learning circle is to solve problems by using its property theorem. Although the problem-solving mode of each question type is not fixed, there are rules to follow. Therefore, to learn the knowledge of the circle well, we must first write more and work hard to solve the problem.

Let's take 20 17-20 18 as an example to see how to solve related problems.

Question 24

The problem (1) is often a basic problem, so don't give up. From the problem condition that AB is the radius of semicircle O, we can get M=90 (the circumferential angle of diameter is 90 degrees), and then we can find the length of AB according to Pythagorean theorem. Since ON=OB (equal radius) and NOB=60, it is concluded that ONB is an equilateral triangle, so the length of NB is equal to the radius OB.

Question (1)

Question (2) is usually difficult, but the grading standard is gradual, so try to write your own ideas. At the same time, no matter how complicated the topic is, the basic knowledge is piled up, so the breakthrough of solving the problem lies in the known conditions. From the topic, we can know that MC is perpendicular to AB, and we can think about the vertical diameter theorem here. Contact P is the midpoint of MN, and we can quickly think of the center line, so that the prototype of the auxiliary line comes out. Finally, transform the application of ideas.

Question (2)

It can't be done overnight, it needs a process. The same is true of the study of circle, so to learn the knowledge of circle well, we must keep practicing and reflecting. Only in this way can we achieve ourselves!