2个回答
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沿ABCDA积分。
A~B,x+y=1,y=-x+1;dy=-dx,x-y=2x-1:
积分=∫(1,0)[(2x-1)dx+1(-dx)]/[x²+(-x+1)²]
=∫(1,0)(2x-2)dx/[2x²-2x+1]
=∫(1,0)(x-1)dx/[x²-x+1/2]
=∫(1,0)(x-1)dx/[(x-1/2)²+1/4]
=∫(1,0){(x-1/2)dx/[(x-1/2)²+1/4]-dx/2[(x-1/2)²+1/4]}
=∫(1,0){2(x-1/2)dx/2[(x-1/2)²+1/4]-d(2x-1)/[(2x-1)²+1]}
=[(1/2)ln[(x-1/2)²+1/4]-arctan(2x-1)](1,0)
=[ln√(x²-x+1/2)-arctan(2x-1)](1,0)
=[ln√(1/2)-arctan(-1)]-[ln√(1/2)-arctan(1)]
=-arctan(-1)+arctan(1)
=π/2
同理,求其他各段,然后相加。
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