4xy-[(x^2+5xy-y^2)-2(x^2+3xy-1/2y^2)]其中:x=-1,y=2

4xy-[(x^2+5xy-y^2)-2(x^2+3xy-1/2y^2)]其中:x=-1,y=2
4xy-[(x^2+5xy-y^2)-2(x^2+3xy-1/2y^2)]其中:x=-1,y=2

4xy-[(x^2+5xy-y^2)-2(x^2+3xy-1/2y^2)]其中:x=-1,y=2
原式=4xy-(x²+5xy-y²-2x²-6xy+y²)
=4xy-(-x²-xy)
=4xy+x²+xy
=x²-5xy
=(-1)²-5×(-1)×2
=11