f(x)=e^x-2x+2a f'(x)=e^x-2 当x≧ln2时，f'(x)≧0，f(x)单调递增 当x＜ln2时，f'(x)＜0，f(x)单调递减 故函数f(x)在x=ln2处取最大值 f(ln2)=2-2ln2+2a
