題目:
A company's total cost for operating its two warehouses is
C(x,y)=√x‧√y-2 thousand dollars,
where x represents the number of units stored at the first warehouse and
y represents the number of units stored at the second. Find the average
cost to store a unit if the first warehouse has between 0 and 4 units,
and the second one has between 3 and 11 units.
參考書的解答我有了,可是我不懂要怎麼寫，而且我看過2個版本
一個是對x定績分求平均值在對y定積分求平均值，所以有2個答案。
另一個版本是對C函數重積分求平均值，只有一個答案。
不知道哪個才正確，煩請高手點解，感恩!
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