一道数学题(不定方程)

y-x-3xy=0,那么5xy(x-y)+15x*y*=?

y-x-3xy=0
x-y=-3xy

5xy(x-y)+15x^2*y^2
=5xy*(-3xy)+15x^2*y^2
=0

解：5xy(x-y)+15x*y*
=5xy(x-y+3xy)
=-5xy(y-x-3xy)
=-5xy×0
=0

5xy(x-y)+15x*y*=5xy(x-y+3xy)=-5xy(y-x-3xy)=-5xy*0=0

提取公因式
5xy(x-y)+15x*y*
=-5xy(y-x-3xy)
=0

多简单的题啊
你上几年级了？
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