Question

若扇形的面积是56cm2,周长是30cm,则半径是

Answer 1

S=nπr²/360=56····················1

C=nπr/180+2r=30················2

联立1、2两式解得：

(15-r)r=56

r²-15r+56=0

(r-7)(r-8)=0

解得：

r=7 或 r=8