来自鲍惠玲的问题
【f(x)二阶可导,g(x)=∫(0,1)f(xt)dt,且limx→0f(x)/x=A问g'(x)在x=0处是否连续】
f(x)二阶可导,g(x)=∫(0,1)f(xt)dt,且limx→0f(x)/x=A问g'(x)在x=0处是否连续
1回答
2020-12-25 05:21
【f(x)二阶可导,g(x)=∫(0,1)f(xt)dt,且limx→0f(x)/x=A问g'(x)在x=0处是否连续】
f(x)二阶可导,g(x)=∫(0,1)f(xt)dt,且limx→0f(x)/x=A问g'(x)在x=0处是否连续
g(x)=∫(0→1)ƒ(xt)dt
令u=xt,du=xdt
t=0,u=0
t=1,u=x
g(x)=(1/x)∫(0→x)ƒ(u)du
g'(x)=(1/x)*ƒ(x)-(1/x²)∫(0→x)ƒ(u)du
g'(0)=lim(x→0)ƒ(x)/x-lim(x→0)[∫(0→x)ƒ(u)du]/x²
=A-lim(x→0)ƒ(x)/(2x)
=A-(1/2)A
=A/2
既然g'(0)存在,则g(x)=0处连续,可导则必定连续.