大一高等数学一道题求详细解释,这类定积分很难理解啊

2025-05-12 16:33:06
推荐回答(1个)
回答(1):

这种题目吧,先把f(t-x)中的x分离出来
令t-x=s
t=s+x
dt=ds
t=0,s=-x
t=x,s=0
g(x)=∫[-x,0] (s+x)^2f(s)ds
=∫[-x,0] (s^2+2sx+x^2)f(s)ds
=∫[-x,0] s^2f(s)ds+∫[-x,0] 2sxf(s)ds+ ∫[-x,0] x^2f(s)ds
=∫[-x,0] s^2f(s)ds+2x∫[-x,0] sf(s)ds+x^2 ∫[-x,0] f(s)ds
g'(x)=-x^2f(x)+2∫[-x,0] sf(s)ds-2x^2f(x)+2x∫[-x,0] f(s)ds-x^2f(x)
=-4x^2f(x)+2∫[-x,0] sf(s)ds+2x∫[-x,0] f(s)ds