问题
选择题
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答案
∵lim △x→0
=3f(x0+3△x)-f(x0) △x lim △x→0
=3f′（x0）=1f(x0+3△x)-f(x0) 3△x
∴f'（x0）=1 3
故选D
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∵lim △x→0
=3f(x0+3△x)-f(x0) △x lim △x→0
=3f′（x0）=1f(x0+3△x)-f(x0) 3△x
∴f'（x0）=1 3
故选D
Look at the picture. It’s a nice 1 . In the picture you can see a teacher’s 2 on his desk. It’s a Chinese book. There are fifty desks and fifty chairs in the room. There is also a big blackboard. You can see a girl and 3 boys. The girl’s 4 is Julia. She is thirteen. The boy with the football is Tom. He likes playing 5 . The other boy is Tony. They 6 the same coats and they are the same age. They look the same. I 7 they are twins. Tom is a 8 boy. A book is in his hand. You 9 see the teacher. 10 is the teacher? He is taking the picture.
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