内接圆柱的半径R,高X
(2-R):X=2:4,
R=2-X/2=(4-X)/2,
圆柱的侧面积S=2∏RX=2∏(4-X)X/2=∏(4-X)X,
S=∏(4-X)X
=∏[4-(2-X)²]
=4∏-∏(2-X)²,
-∏(2-X)²