A.8 B.4 C.2 D.6

3:6=5: 10 6:3= 10:5

(2) In the numbers of 2, 5, 1/3, add a number to form a ratio, and the following cannot be used as an addend (c).

C. Two fifths D. Five sixths

(3) Cut the circle into an approximate rectangle, and compare the perimeter of the rectangle with the perimeter (d) of the circle.

A. Enlarge B. Reduce C. Enlarge 9 times D. Increase

(4) The area of a sector with a central angle of 90 is equal to the area of a circle, so the sector radius is (a) of the circle radius.

A.2 times B. Half C.π times D. equals

⑤ In the same circle, the arc length of the sector changes with the change of the central angle. If the central angle is enlarged by 3 times, the arc length (b) will be.

A. unchanged B. zoom in 3 times C. zoom in 9 times D. zoom out 9 times

6. The sector radius is 100 m and the central angle is 18. In the following calculation, the error is (d).

A. arc length l=3 1.4

B. Sector area S= 1570 m2

The area of circle c is S=3 1400 square meters.

D. Sector circumference c =131.4m.