∴f′(x)=ex-2,x∈R.
令f′(x)=0,得x=ln2.
于是當(dāng)x變化時(shí),f′(x),f(x)的變化情況如下表:
x | (-∞,ln2) | ln2 | (ln2,+∞) |
f′(x) | - | 0 | + |
f(x) | 單調(diào)遞減 | 2(1-ln2+a) | 單調(diào)遞增 |
單調(diào)遞增區(qū)間是(ln2,+∞),
f(x)在x=ln2處取得極小值,
極小值為f(ln2)=eln2-2ln2+2a=2(1-ln2+a),無(wú)極大值.
(Ⅱ)證明:設(shè)g(x)=ex-x2+2ax-1,x∈R,
于是g′(x)=ex-2x+2a,x∈R.
由(1)知當(dāng)a>ln2-1時(shí),
g′(x)最小值為g′(ln2)=2(1-ln2+a)>0.
于是對(duì)任意x∈R,都有g(shù)′(x)>0,所以g(x)在R內(nèi)單調(diào)遞增.
于是當(dāng)a>ln2-1時(shí),對(duì)任意x∈(0,+∞),都有g(shù)(x)>g(0).
而g(0)=0,從而對(duì)任意x∈(0,+∞),g(x)>0.
即ex-x2+2ax-1>0,
故ex>x2-2ax+1.