高数问题。 10
1个回答
2017-09-13
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1.证明∫(0→π)xf(sinx)dx=(π/2)∫(0→π)f(sinx)dx
令x=π-u,dx=-du
当x=π时,u=0
当x=0时,u=π
∫(0→π)xf(sinx)dx
=∫(π→0)(π-u)f[sin(π-u)]*(-du)
=∫(0→π)(π-u)f[sin(π-u)]du
=∫(0→π)πf[sin(π-u)]du-∫(0→π)uf[sin(π-u)]du
=π∫(0→π)f(sinu)du-∫(0→π)uf(sinu)du
令x=π-u,dx=-du
当x=π时,u=0
当x=0时,u=π
∫(0→π)xf(sinx)dx
=∫(π→0)(π-u)f[sin(π-u)]*(-du)
=∫(0→π)(π-u)f[sin(π-u)]du
=∫(0→π)πf[sin(π-u)]du-∫(0→π)uf[sin(π-u)]du
=π∫(0→π)f(sinu)du-∫(0→π)uf(sinu)du
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