1.f(x)=x+1/（x+1）=（x+1)+1/(x+1)-1>=2-1=1,当x=0时取等号，∴它的最小值=1.2.0当x=1/6时它取最大值1/12.
f(x)=x+1/（x+1）=x+1 + 1/(x+1) -1≥2√(x+1)/(x+1) -1=1y=x(1-3x)=3 x(1/3-x)≤3 [(x + 1/3 - x)/2]^2=3 * 1/36=1/12
