圆台上下底面半径r,R,侧面积等于两底面积之和,圆台母线长＝

设圆台母线长为X,展开的扇形大圆弧半径为R1,小圆弧半径为R2.则：X=R1-R2PI*R^2+PI*r^2=2*PI*R*R1/2-2*PI*r*R2/2=PI*R*R1-PI*r*R2R^2+r^2=R*R1-r*R2R2=(R*R1-R^2-r^2)/r2*PI*R/R1=2*PI*r/R2R/R1=r/R2R1/R=R2/r=(R*R1-...