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令a=1+√x
x=a²-2a+1
dx=(2a-2)da
x=1,a=2
x=4,a=3
所以原式=∫(2,3)2ada/(2a-2)(a-1)²
=∫(2,3)ada/(a-1)³
令a/(a-1)³=m/(a-1)+n/(a-1)²+p/(a-1)³
则a=m(a²-2a+1)+n(a-1)+p
解得m=0,n=1,p=1
s所以原式=∫(2,3)[1/(a-1)²+1/(a-1)³]da
=-1/(a-1)-1/[2(a-1)²] (2,3)
=-1/2-1/8+1+1/2
=7/8
x=a²-2a+1
dx=(2a-2)da
x=1,a=2
x=4,a=3
所以原式=∫(2,3)2ada/(2a-2)(a-1)²
=∫(2,3)ada/(a-1)³
令a/(a-1)³=m/(a-1)+n/(a-1)²+p/(a-1)³
则a=m(a²-2a+1)+n(a-1)+p
解得m=0,n=1,p=1
s所以原式=∫(2,3)[1/(a-1)²+1/(a-1)³]da
=-1/(a-1)-1/[2(a-1)²] (2,3)
=-1/2-1/8+1+1/2
=7/8
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