(x+3)²+|y-1/3|=0
(x+3)²=0,|y-1/3|=0
x=-3
y=1/3
（2x²-5xy）-3（x²-y²）+x²-3y²
=2x²-5xy-3x²+3y²+x²-3y²
=2x²+x²-3x²-5xy+3y²-3y²
=-5xy
=-5*(-3)*1/3
=5