a b c⒈已知abc=1,求_______+_________+_________的值.ab+a+1 bc+b+1 a
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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
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 a](/uploads/image/z/19678390-70-0.jpg?t=a+b+c%E2%92%88%E5%B7%B2%E7%9F%A5abc%3D1%2C%E6%B1%82_______%2B_________%2B_________%E7%9A%84%E5%80%BC.ab%2Ba%2B1+bc%2Bb%2B1+a)
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
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
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