第三题X+y的范围是怎么出来的？高等数学
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(x+y)^-3分之（2a）^-1
=2a分之（x+y)³
x^2(x-1)^-1-[1+（x^2-x)^-1]
=x²/(x-1)-[1+1/(x²-x)]
=x²/(x-1)-(x²-x+1)/x(x-1)
=(x³-x²+x-1)/x(x-1)
=[x²(x-1)+(x-1)]/x(x-1)
=(x-1)(x²+1)/x(x-1)
=(x²+1)/x
7^-1(x+y)(x-y)^-2
=(x+y)/[7(x-y)²]
=2a分之（x+y)³
x^2(x-1)^-1-[1+（x^2-x)^-1]
=x²/(x-1)-[1+1/(x²-x)]
=x²/(x-1)-(x²-x+1)/x(x-1)
=(x³-x²+x-1)/x(x-1)
=[x²(x-1)+(x-1)]/x(x-1)
=(x-1)(x²+1)/x(x-1)
=(x²+1)/x
7^-1(x+y)(x-y)^-2
=(x+y)/[7(x-y)²]
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