有3D Model的問題不太懂，望有題解

如題。基本上我做到a part，不過到b part我就不明白了...但是答案只有答案一個....沒題解...

希望各位能幫幫我。

怕大家看不清楚字，我寫一寫。

18. Figure 9(a) shows a chocolate cake VABCD placed on a horizontal table. The cake is in the shape of a regular square pyramid and all its lateral faces are uniformly covered with cream. It is given that VA=8 cm and AB=10 cm.


(a) Find
(i) angle VAB
(ii) the angle between the plane VAB and ABCD

(b) As shown in Figure 9(b), the cake is then cut into two parts along the plane EFCD, where E and F are points on VA and VB respectively such that EF // AB. The part VEFCD is removed. It is know that the angle between the planes EFCD and ABCD is 30 degree.

(i) Find AE.
(ii) Samantha claims that ' More than 30% of the cream is removed.' Is her claim correct? Explain your answer.


圖片參考：http://imgcld.yimg.com/8/n/HA00132844/o/20121224155125.jpg