括号打少一半,麻烦出了一堆4A+{2B-[5A-（3B-2C)+6B]+3C}=4A+[2B-(5A-3B+2C+6B)+3C]=4A+2B-5A+3B-2C-6B+3C=-A-B+C代入ABC原式=-(2a+3)-(-4a2+3a-1)+(3a2-4a+4)=-2a-3+4a2-3a+1+3a2-4a+4=7a^2-9a+2