原式=0.6-x-0.6x+x2
=x2-1.6x+0.6
原式=2x2-2xy+xy-y2
=2x2-xy-y2
原式=2n2-6n+5n-15
=2n2-n-15
原式=acx2+adx+bcx+bd
=acx2+(ad+bc)x+bd
原式=(x2-2xy-xy+2y2)-(1/2)(2x2+4xy-3xy-6y2)
=(x2-3xy+2y2)-(1/2)(2x2+xy-6y2)
=x2-3xy+2y2-x2-(1/2)xy+3y2
=-(7/2)xy+5y2
将x=2,y=5带入得：-(7/2)*2*5+5*5*5
=90