每日一题 | A-Level数学 Integration by parts，同学们快来做题打卡吧！

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【A-Level数学 Integration by parts】

Integration by parts：

Use Integration by parts to find ∫xsin3x dx ；

Using your answer to part 1,find ∫x^2cos3x dx。

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昨日 [ 每日一题 ] 答案

With reference to the relevant type of elasticity of demand, explain the terms (I) inferior good, and (ii) complementary good.

题目分析：

该题考察了YED和XED的取值问题。答题结构：

①首先给出ED（需求弹性）的概念：Elasticity of demand concerns the responsiveness of demand to a change in a variable.

②然后使用YED和XED分别讨论两种商品的性质：An inferior good is one that is bought in smaller quantities as income rises, as it is replaced by a superior good.

It involves income elasticity which has a negative value.

An example might be motor cycles replaced by cars.

Complementary goods are ones that are jointly demanded, such as coffee and cream.

Cross price elasticity of demand is relevant and is negative as the rise in price of one good reduces the quantity demanded of a complement.