a²-2ab=-10
b²-2ab=16
两式相加
a²-4ab+b²=6
-a²+4ab-b²=-6
P-[Q-2P-(-P-Q)]
=P-[Q-2P+P+Q]
=P-(2Q-P)
=2P-2Q
=2(a²+3ab+b²)-2(a²-3ab+b²)
=12ab
=12*1*(-1)
=-12
2(3x-y)-4(3x-y)+5(3x-y)-6(3x-y)
=6x-2y-12x+4y+15x-5y-18x+6y
=-9x+3y
=-9*(-5/12)+3*(-1/4)
=15/4-3/4
=12/4
=3