若x+y=3,则x²-y²+6y=急

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若x+y=3,则x²-y²+6y=急
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若x+y=3,则x²-y²+6y=急
若x+y=3,则x²-y²+6y=
急

若x+y=3,则x²-y²+6y=急
答：
x+y=3
x²-y²+6y
=(x-y)(x+y)+6y
=3(x-y)+6y
=3x-3y+6y
=3x+3y
=3(x+y)
=3*3
=9

x^2-y^2+6y=(x+y)(x-y)+6y=3(x-y)+6y=3x-3y+6y=3(x+y)=9