设拱形所在的扇形角度为x、扇形半径y则y² = (y-2.25)² + (4.242/2)² 可求出 y=2.12则 sin(x/2) = 4.242/2y sin(x/2) = 1 可求出 x=180故 拱形周长是(x/180)*π*y =（π x y）/180 =π y=3.14*2.12=6....