[(3x+y)²-3(3x-y)(x+y)-(x-3y)(x+3y)]÷(2xy)
=[(9x²+6xy+y²)-3(3x²+2xy-y²)-(x²-9y²)]÷(2xy)
=(9x²+6xy+y²-9x²-6xy+3y²-x²+9y²)÷(2xy)
=(13y²-x²)÷(2xy)
=(13×4-4分之1)÷[2×2分之1×(-2)]
=51又4分之3÷(-2)
=51.75÷(-2)
=-25.875

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