1.f'(x) = e^x - a
(1) a ≤ 0时
e^x > 0,f'(x) > 0
f(x)在(-∞,+∞)内单调递增
(2) a > 0时
f'(x) = e^x - a = 0
x = lna
x < lna时,f'(x) < 0,f(x)单调递减
x > lna时,f(x) > 0,f(x)单调递增
2.
(1)a ≤ 0时,f(0) = 1,f(x) ≥0显然成立
(2) a > 0时,须极值点在y轴左侧(lna < 0,a < 1),且f(0) ≥0
f(0) = 1 > 0显然成立,a < 1结合前提:0 < a < 1
结合(1)(2):a < 1