設(shè)f(x)是連續(xù)函數(shù),F(xiàn)(x)是f(x)的原函數(shù),則( ?。?br/>A. 當(dāng)f(x)是奇函數(shù)時,F(xiàn)(x)必是偶函數(shù)
B. 當(dāng)f(x)是偶函數(shù)時,F(xiàn)(x)必是奇函數(shù)
C. 當(dāng)f(x)是周期函數(shù)時,F(xiàn)(x)必是周期函數(shù)
D. 當(dāng)f(x)是單調(diào)增函數(shù)時,F(xiàn)(x)必是單調(diào)增函數(shù)
(1)選項B,設(shè)f(x)=x
2,它是偶函數(shù),f(x)的原函數(shù)是F(x)=
x3+C(C為任意常數(shù)),但F(x)并不是奇函數(shù)(除了C=0外),所以排除B.
(2)選項C,設(shè)f(x)=sin
2x,但它的原函數(shù)F(x)=
x?sin2x+C(C為任意常數(shù))不是周期函數(shù),所以排除C.
(3)選項D,設(shè)f(x)=x,它是R上的增函數(shù),但它的原函數(shù)F(x)=
x2+C(C為任意常數(shù)),不是R上的增函數(shù),所以排除D.
(4)選項A,由題意設(shè)
F(x)f(t)dt+C(C為任意常數(shù)),則
F(?x)f(t)dt+C-
f(?u)du+C,
∴如果f(x)是奇函數(shù),則有f(-u)=-f(u)
∴F(-x)=
f(u)du+C=F(x),選項A正確.
故選:A.