第5个回答 2020-11-14
f(x)
= ∫(0,x) (a+bx)g(t)dt
=∫(0,x) ag(t)dt + x∫(0,x) bg(t)dt
f'(x)
= ag(x)dx +x'∫(0,x) bg(t)dt +x [∫(0,x) bg(t)dt]'
= ag(x)dx + ∫(0,x) bg(t)dt + xbg(x)
所以:
G(n) = ∫(0,n) (ar-br-bn+br+cn-cr)P(r)dr + ∫(n,∞) (a-b)nP(r)dr
= ∫(0,n) (a-c)rP(r)dr
- n∫(0,n) (b-c)P(r)dr
+ n∫(n,∞) (a-b)P(r)dr
G'(n) = (a-c)nP(n)
- ∫(0,n) (b-c)P(r)dr - n(b-c)P(n)
+∫(n,∞) (a-b)P(r)dr - n(a-b)nP(n)
=(a-c-b+c-a+b)nP(n) - ∫(0,n) (b-c)P(r)dr +∫(n,∞) (a-b)P(r)dr
= -(b-c)∫(0,n) P(r)dr +(a-b)∫(n,∞) P(r)dr