扇形弧长C=xr
锥形底圆半径R=C/(2π)=xr/(2π)
锥形母线=r
锥形高H=√(r^2-R^2)=√{r^2-[xr/(2π)]^2}
锥形的容积V=R^2Hπ/3
=[xr/(2π)]^2√{r^2-[xr/(2π)]^2}π/3