A=3a^2+6ab-b^2,B=2b^2-5ab+ac,C=-4a^2-ab+b^2,∴A-［B-(A-2C+3B)］-(A-B)=A-［-2B-A+2C］-A+B=A+2B+A-2C-A+B=A+3B-2C=(3a^2+6ab-b^2)+3(2b^2-5ab+ac)-2(-4a^2-ab+b^2)=11a^2-7ab+3b^2+3ac.=37/4-3/2c
