第1个回答 2016-11-24
y= 2x + 8/x
x->0+ , y-> +∞
x->0- , y-> -∞
y' = 2 - 8/x^2
y'=0
2 - 8/x^2=0
2x^2-8=0
x=1/2 or -1/2
y'' = 16/x^3
y''(1/2) >0 (min)
y''(-1/2)< 0 (max)
y(1/2) = 1 + 4 =5
y(-1/2)= -1 -4 =5
单调
增加 (-∞ ,-1/2] U [1/2, +∞)
减小 [-1/2 , 0)U (0, 1/2]