=2zh+4元r-2rh2=0 Or 2πr-Zr2=0 →h=2r Ch aL 4 a入 -rh+30 2-3 此时圆柱体的表面积为 2-3此时圆柱体的表面积为 2 2 2 4 2 0 2 0 2 4 0 3 L h r rh r L r r h r h L r h        = + − =       = − =  =     = − + =    . 3 2  r = 3 3 3 2 h = 2 3 2 3 2 6       