Assume h(x) and k(x) have continuous derivatives on [a, b]

Joanna Benson

Joanna Benson

Answered question

2021-12-11

Assume h(x) and k(x) have continuous derivatives on [a, b] and derive the integration-by-parts formula
abh(t)k(t)dt=h(b)k(b)h(a)k(a)abh(t)k(t)dt

Answer & Explanation

amarantha41

amarantha41

Beginner2021-12-12Added 38 answers

Step 1
Let u,v be two functions of t
Using product rule
d(uv)=udv+vdu
Integrating on both sides
d(uv)=udv+vdu
uv=udv+vdu
udv=uvvdu
Step 2
Consider
abh(t)k(t)dt
Let
u=h(t)
dv=k'(t)=> v=k(t)
Using integration by parts
abh(t)k(t)dt=[h(t)k(t)]ababk(t)h(t)dt
abh(t)k(t)dt=h(b)k(b)h(a)k(a)abk(t)h(t)dt

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