When deducing the area formula of a circle, the circle is divided into several equal parts to form an approximate rectangle. The length of the rectangle is 6.42cm more than the width, and the area is? In the derivation of the area formula of a circle, the circle is divided into several equal parts to form an approximate rectangle. The length of the rectangle is 6.42cm more than the width, and the area is ()

When deducing the area formula of a circle, the circle is divided into several equal parts to form an approximate rectangle. The length of the rectangle is 6.42cm more than the width, and the area is? In the derivation of the area formula of a circle, the circle is divided into several equal parts to form an approximate rectangle. The length of the rectangle is 6.42cm more than the width, and the area is ()

First of all, you need to understand how the "Rectangle" is spelled out. Then, you need to know the connection between the length and width of the "Rectangle" and the original circle: (1) length: the half circumference of the circle; that is: π R; (2) width: the radius of the circle; that is: R; the following formula is OK: π R - r = 6.4

When Xiaoqiang deduces the area formula of a circle, he divides the circle into several equal parts and forms an approximate rectangle. It is known that the length of the rectangle is 12.56 cm
What is the area of the round piece of paper he used

The length of the long side of the rectangle = half of the circumference of the circle - the circumference of the circle = 12.56 * 2 = 25.12 cm - the diameter of the circle = 25.12 / 3.14 = 8 cm - the radius of the circle = 4 cm - the area of the circle = 3.14 * 4 * 4 = 50.24 square cm

In the derivation of the area formula of a circle, the circle is divided into several parts to form a rectangle. The length of the rectangle is 12.56 cm, and the area of the circle is ()

Radius of circle = 12.56 △ 3.14 = 4cm
therefore
Area of circle = 3.14 × 4 square = 50.24 square centimeter

The formula of circumference, area, diameter and radius in letters

2πr

The first volume, the second volume of mathematics knowledge points of each chapter

Rational number (operation, absolute value), algebraic formula (integral addition and subtraction), equation, graph (three views), plane graph (line, angle, parallel, vertical)
Plane figure 2 (triangle, polygon, inner angle sum), power operation, factorization, equations, inequalities, proof (reciprocal proposition)

As shown in the figure, ⊙ o with a waist ab of isosceles △ ABC as the diameter intersects BC at D and makes de ⊥ AC at e through D, we can draw the conclusion that De is the tangent of ⊙ O. question: (1) if point O moves to point B on AB, the condition that a circle with o as the center and ob length as the radius still intersects BC at D and de ⊥ AC remains unchanged, then is the above conclusion true? (2) if AB = AC = 5cm, Sina = 35, then where is the center O of the circle at AB and ⊙ o tangent to AC?

(1) The reasons are as follows: as shown in the figure, connect OD; ∵ od = ob, ∵ ABC = ∠ ODB, ∵ AB = AC, ∵ ABC = ∠ ACB, ∵ ACB = ∠ ODB, ∵ OD ‖ AC; and ∵ de ⊥ AC,