(2分之3x的2次方-5xy+y的2次方)-【-3xy+2(4分之一x的2次方-xy)+3分之2y的2次方】
=3/2x²-5xy+y²-(-3xy+1/2x²-2xy+2/3y²)
=3/2x²-5xy+y²+5xy-1/2x²-2/3y²
=x²-1/3y²
(3/2x^2-5xy+y^2)-[-3xy+2(1/4x^2-xy)+2/3y^2]
=3/2x²-5xy+y²+3xy-2/3y²+1/2x²-2xy
=2x²-4xy+1/3y²
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