1, a circular scissors is spliced into an approximate trapezoid, and the circumference of this trapezoid is about 2 1.42CM (this should be composed of circumference plus two radii, so it is 2π r+2 r), so the radius of the circle is 2 1.42/(2π+2) about 2.52.

2. What about the pictures?

3. What about the pictures?

4. If a piece of cylindrical wood is cut into two sections along the cross section, its surface area will increase by 28.26 square centimeters.

So the section radius is r = sqrt (28.26/2/ π) =sqrt (4.5).

If it is divided into two semi-cylinders along the diameter, the surface area will increase by 100 cm2.

So the height of the cylindrical wood is h =100/2/2r = 25/sqrt (4.5));

The original surface area of the cylinder is 2 π r× h+28.26/2 = 50 π+14.13 =171.13.