|
设$\,f,g\,$单调且可积$,\,g'\,$存在,令$\,F(x)=\displaystyle\int_a^xf(t)dt.\quad\because\,g'\,$不变号,?+!xV 据第一中值定理,$\,\displaystyle\int_a^bfg=gF\bigg|_a^b-\int_a^bFg'=g(b)\int_a^bfdVE -F(\xi)\int_a^bg'$Tg31 $\therefore\qquad\boxed{\int_a^bf(x)g(x)dx=g(a)\int_a^{\xi}f(x)dx+g(b)\int_{\xi}^bf(x)dx}$Iqd
| | |
|
|