a b c⒈已知abc=1,求_______+_________+_________的值.ab+a+1 bc+b+1 ac+c+1⒉求值:a-b a的平方+b的平方_______- ______________________2a+2b a的平方-b的平方2x-3 A B⒊已知__________=_______+_______求A、B的值.(x-1)(x+2) x-1 x+2那

a b c⒈已知abc=1,求_______+_________+_________的值.ab+a+1 bc+b+1 ac+c+1⒉求值:a-b a的平方+b的平方_______- ______________________2a+2b a的平方-b的平方2x-3 A B⒊已知__________=_______+_______求A、B的值.(x-1)(x+2) x-1 x+2那
a b c
⒈已知abc=1,求_______+_________+_________的值.
ab+a+1 bc+b+1 ac+c+1
⒉求值:
a-b a的平方+b的平方
_______- ______________________
2a+2b a的平方-b的平方
2x-3 A B
⒊已知__________=_______+_______求A、B的值.
(x-1)(x+2) x-1 x+2
那些符号和数字顺着横线1个个对回去就OK了，
比如:
a b c
_______+___________________+____________
ab+a+1 bc+b+1 ac+c+1

a b c⒈已知abc=1,求_______+_________+_________的值.ab+a+1 bc+b+1 ac+c+1⒉求值:a-b a的平方+b的平方_______- ______________________2a+2b a的平方-b的平方2x-3 A B⒊已知__________=_______+_______求A、B的值.(x-1)(x+2) x-1 x+2那
1.因为：abc=1
a/ab+a+1= a/ab+a+abc= 1/bc+b+1
c/ca+c+1= c/(1/b)+c+1= bc/bc+b+1
所以：
原式
= a/(ab+a+1)+ b/(bc+b+1)+ c/(ca+c+1)
= 1/(bc+b+1)+ b/(bc+b+1)+ bc/(bc+b+1)
= bc+b+1/bc+b+1
= 1
2.(a-b)/(2a+2b)-(a^2+b^2)/(a^2-b^2)
=(a-b)²/[2(a-b)(a+b)]-2(a²+b²)/[2(a-b)(a+b)]
=-(a+b)²/[2(a-b)(a+b)]
=-(a+b)/[2(a-b)]
3.已知(2x-3)/(x-1)(x+2)=A/(x-1)+B/(x+2),求A、B的值.
A/(x-1)+B/(x+2)
=A(x+2)/(x+2)(x-1)+B(x-1)/(x+2)(x-1)
=[A(x+2)+B(x-1)]/(x+2)(x-1)
=[(A+B)x+(2A-B)]/(x+2)(x-1)=2x-3/[(x-1)(x+2)]
A+B=2,2A-B=-3
3A=-1
A=-1/3
B=2+1/3=7/3

确实有些乱，重写一下吧！！

这是什么意思？

1。不妨令a=b=c=1,代入a/(ab+a+1)+b/(bc+b+1)+c/(ac+c+1)=1/3+1/3+1/3=1
2。(a-b)/(2a+2b)-(a^2+b^2)/(a^2-b^2)
=(a-b)²/[2(a-b)(a+b)]-2(a²+b²)/[2(a-b)(a+b)]
=-(a+b)²/[2(a-b)(a+b)]

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1。不妨令a=b=c=1,代入a/(ab+a+1)+b/(bc+b+1)+c/(ac+c+1)=1/3+1/3+1/3=1
2。(a-b)/(2a+2b)-(a^2+b^2)/(a^2-b^2)
=(a-b)²/[2(a-b)(a+b)]-2(a²+b²)/[2(a-b)(a+b)]
=-(a+b)²/[2(a-b)(a+b)]
=-(a+b)/[2(a-b)]
3。右边通分后分子=A(x+2)+B(x-1)=（A+B)x+(2A-B)
左边分子=2x-3
由于分母一样，分式相等，所以有：A+B=2，2A-B=-3
解得A=-1/3,B=7/3

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