Fill in the blanks.

Divide a circle into several equal parts and cut it into an approximate rectangle. The length of this rectangle is equivalent to (? ), the width of the rectangle is round (? )。 Because the area of a rectangle is () and the area of a circle is ().

A circle has a diameter of 6 cm, a circumference of () and an area of (? )。

The circumference of a circle is 25. 12 decimeter, and the area is (? )。

The radius of circle A is three times that of circle B, and the circumference of circle A is (? ), the area of circle A is the area of circle B (? )。

The radius of a circle is 8 cm, and the area of 3/4 of this circle is () square cm.

Rectangular, square, circular, (? ) the largest area.

Application problems.

There is a sheep tied to a stump on the grass. The length of this rope is 4 meters. How many square meters of grass can this sheep eat at most?

After the Grenade explodes, the radius of effective killing range is 8 meters, and the effective killing area is how many square meters?

The aluminum basin is stamped from a circular aluminum plate with a diameter of 30 cm. How many square meters of aluminum plate does it take to make 1000 such pots?