函数f（x）=x3+x（x∈R）（ ）
A．是奇函数且在（-∞，+∞）上是增函数
B．是奇函数且在（-∞，+∞）上是减函数
C．是偶函数且在（-∞，+∞）上是增函数
D．是偶函数且在（-∞，+∞）上是减函数
f（-x）=（-x）3+（-x）=-x3-x=-f（x）
∴函数f（x）是奇函数，
∵f′（x）=3x2+1＞0
∴函数f（x）在区间（-∞，+∞）上是增函数．
故选A．
| 阅读下面对话，从方框内选择恰当的句子完成此对话，并将其标号填入题前括号内。 （其中有两项是多余选项）。 | |
B: Sorry. (1)_______________. There are many rules in my house. A: What rules do you have? B: My mother asks me to go home by five o'clock. A: (2)_______________. B: No, I can't. A: Do you have to practice your guitar every day? B: Yes, I do. (3)_______________. I don't like it. Do you have any rules in your family? A: Yes, I can't watch TV on school nights, either. B: (4)_______________. A: I have to be in bed by 9: 30. B: (5)_______________. A: Yes, I have to clean my bedroom and help Mother buy something. |
