题目内容

不定积分∫xf"(x)dx等于______。

A. xf"(x)-f"(x)+C
B. xf"(x)-f(x)+C
C. xf"(x)+f"(x)+C
D. xf"(x)+f(x)+C

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增值税税率是17%的商品是______

A. 粮食
B. 食用植物浊
C. 煤炭
D. 原油

若f(x)的一个原函数是e-2x，则∫f"(x)dx=______。

A. e-2x+C
B. -2e-2x
C. -2e-2x+C
D. 4e-2x+C

Directions: In this section, you will hear 6 short conversations. At the end of each conversation, a question will be asked about what was said. Both the conversation and the question will be read only once. After each question, there will be a pause. During the pause, you must read the three choices marked A, B and C, and decide which is the best answer.

A. $1.40.
B. $8.60.
C. $4.30.

设函数f(x)在(-∞，+∞)上是偶函数，且在(0，+∞)内有f"(x)＞0，f"(x)＞0，则在(-∞，0)内必有______。

A. f"(x)＞0，f"(x)＞0
B. f"(x)＜0，f"(x)＞0
C. f"(x)＞0，f"(x)＜0
D. f"(x)＜0，f"(x)＜0