Question

请数学大神解答这几道数学题？

Answer 1

(5)
lim(△x->0)[ f(x0+2 △x) -f(x0) ]/△x
=2f'(x0)
=2k
ans :B
(6)
连续是可导的 （B）必要条件
(7)
y=ln(1-2x)
y'=-2/(1-2x)
ans : D
(8)
f'(x) >0 => f(x) 递增
f''(x)<0 => f'(x) 递减
ans :B
(9)
y=sinx/x^2
y' = (x^2.cosx - 2xsinx)/x^4
ans: D
(10)
f(x) =(1/3)x^3-x
f'(x) = x^2-1
f'(x)=0
x^2-1=0
x=1 or -1
f''(x) = 2x
f''(1)=2 >0 (min)
f(1)= 1/3 -1 =-2/3
f(-2)= -8/3 +2 = -2/3
f(2) = -8/3 -2 = -14/3
ans : A

追问

前5道题呢？不用过程，只要答案就行，谢谢大神

追答

(5) B
(6) B

(7) D

(8) B

(9) D

(10) A

追问

谢谢，可是1-4题答案呢？

追答

(1)
y=x+e^x
y'= 1+e^x
y'|x=0 = 2
切线方程 (0,1)
y-1= 2x
2x-y+1=0
ans: A
(2)
f(x)= ax^2+b
f'(x)= 2ax
f'(x) >0
=> a>0
ans: B
(3)
f(x) =1/x
f'(x) = -1/x^2 <0
ans :D
(4)
ans :A