解：2（x+y)(x+y)-(x-y)²+（x-y)²=2(x+y)²-[(x-y)²-(x-y)²]=2(x²+2xy+y²)-0=2x²+4xy+2y²当x=2,y=1/2时，原式=2×2²+4×2×½+2×（½）²=8+4+½=12.5
=2(x+y)²当x=2,y=1/2时，原式=4.5
