4x²-[2x-(x²-2x+3)-2(x²-3x)]
=4x²-2x+(x²-2x+3)+2(x²-3x)
=4x²-2x+x²-2x+3+2x²-6x
=7x²-10x+3

(x²-2xy+y²)-2(x²+2xy+y²)
=x²-2xy+y²-2x²-4xy-2y²
=-x²-6xy-y²