(3a+b)(3a-b)+3(a-2b)²+(-3a)(4a-3b)=9a²-b²+3(a²-4ab+b²)-12a²+9ab=9a²-b²+3a²-12ab+3b²-12a²+9ab=2b²-3ab当a=-1,b=-2时原式=8-6=2,6,