图
f(x)＝2－x－1/(x+1)f'(x) = -1 + 1/(x+1)^2 f'(x) =0(x+1)^2 -1=0x+1 = 1 or -1x=0(rej) or -2f''(x)=-2/(x+1)^3 >0 (min)min f(x) = f(-2) = 2+2 －1/(-2+1) = 5
