高三函数单调性的题

1.设f(x)=e^x-1-x-x^2/2f'(x)=e^x-1-xf''(x)=e^x-1若x>=0,f''(x)=e^x-1>=0,f'(x)是增函数,所以f'(x)>=f'(0)=0,即f(x)是增函数当x>0,f(x)>f(0)=0e^x-1-x-x^2/2>0,e^x>1+x+x^2/22.(x-1)f'(x)>=0当x>=1,f'(x)>=0,f(x)是增函数,f(2)>=f(1)当x<=1,f'(x)<=0,f(x)是减函数,f(0)>=f(1)f(0)+f(2)>=2f(1)答案C 收起