The formula of circular area is a theorem. Is the square of pi * radius, which can be expressed in letters as: S=πr? Or s = π (d/2)? . (π stands for π:3. 14 15926 ..., r stands for radius and d stands for diameter).
Divide the circle into several parts evenly and you can make an approximate rectangle. The width of the rectangle is equal to the radius (r) of the circle, and the length of the rectangle is half the circumference (c) of the circle. The area of a rectangle is a×b, and the area of a circle is: the radius (r) of the circle times the half circumference c, and S=r×(C/2)=r×(2r×π/2)=r2×π.
Perimeter (c): the diameter (d) of a circle. If the circumference (c) of a circle divided by the diameter (d) of the circle equals π, then the meaning of multiplication equals π times the diameter (d) of the circle, and c = π d. The diameter (d) of the same circle is twice the radius (r) of the circle, so the circumference (c) of the circle equals 2 times π times the radius (r) of the circle, and c = 2π r.
The benefits of learning mathematics:
1. Mathematics can cultivate people's integrity and honesty. Mathematics pays the most attention to convincing people by reasoning, and only believes in the results of logical reasoning.
Mathematics can cultivate people's tenacity and courage. Paulia, a great math educator, thinks that difficulties and problems belong to the same concept. If there is no difficulty, there will be no problem.
3. Mathematics can cultivate people's overall consciousness. To solve mathematical problems, we must comprehensively consider the problems from the known to the conclusion and grasp the interrelationships of all aspects. Mathematics teaching can cultivate students to consider problems comprehensively from the overall situation.