2. "Cut a circular piece of paper into several parts" should be cut into a small fan with the original center as the vertex and the radius =r as the radius;
"Assemble into approximate rectangle" should take the radius of the sector as the width of the rectangle, and arrange the vertices and arcs of the sector in turn to form an approximate rectangle;
The length of a rectangle is equal to half the circumference.
∴8.28÷2=(3. 14+ 1)r
∴r= 1(cm)
∴ s = 3.14×/kloc-0 /×1= 3.14 (square centimeter)
This answer should be reasonable, have a look!
3. Shortening 0.3 14 means that the perimeter is reduced by 0.3 14, and the perimeter formula c = 2π r. When c is reduced by 0.3 14, let an invagination x, that is, the radius is reduced by x, and substitute it into the formula c-0.314 = 2π * (r
C-0.3 14=2πr-2πx and because c=2πr, 2πr is replaced by C, it becomes C-0.314 = C-2π x.
So x=0.05.
That is, invagination is 0.05cm.