A.2:1B.1:2c.4:1

2。 Circle the following picture with wire of equal length, in which (c) has the largest area.

Answer: Rectangular, square and round.

3。 A semicircle with radius r and perimeter (c)

A.2π rx1/2b.π r+r c.π r+2r d.2π r+2r

4。 The function range of an automatic rotary sprinkler irrigation device on the park lawn is 8M, and the area it can spray irrigation is (C).

Answer: 50.24 m2 b. 100.48 m2 C.200.96M2.

5. A circle, the diameter of the outer circle is 10CM, the radius of the inner circle is 2CM, and the area of this circle is (B )CM2.

A.3. 14X( 10 square -2 square)

B.3. 14X(5 square -2 square)

C.3. 14X( 10-2 square)

D.3. 14X(5-2 square)