已知:x+y=12,xy=9,则x²y+2xy²分之x²+3xy+2y²=
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x²y+2xy²分之x²+3xy+2y²=
=(x+2y)(x+y)/xy(x+2y)
=(x+y)/xy
=12/9
=4/3
=(x+2y)(x+y)/xy(x+2y)
=(x+y)/xy
=12/9
=4/3
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(x²+3xy+2y²)/(x²y+2xy²)
=(x²+2xy+y²+xy+y²)/(x²y+2xy²)
=[(x+y)²+y(x+y)]/[xy(x+2y)]
=(x+y)[(x+y)+y]/[xy(x+2y)]
=(x+y)(x+2y)/[xy(x+2y)]
=(x+y)/(xy)
=12/9
=4/3
=(x²+2xy+y²+xy+y²)/(x²y+2xy²)
=[(x+y)²+y(x+y)]/[xy(x+2y)]
=(x+y)[(x+y)+y]/[xy(x+2y)]
=(x+y)(x+2y)/[xy(x+2y)]
=(x+y)/(xy)
=12/9
=4/3
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(x²+3xy+2y²)/(x²y+2xy²)
=[(x+2y)(x+y)]/[xy(x+2y)]
=(x+y)/xy
=12/9
=4/3
=[(x+2y)(x+y)]/[xy(x+2y)]
=(x+y)/xy
=12/9
=4/3
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那就：
(x²y+2xy²)/(x²+3xy+2y²)
=xy(x+2y)/[(x+2y)(x+y)]
=xy/(x+y)
=9/12
=3/4
思路就是因式分解，然后约分，思路还是不变的。
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