(1)a-[4b-c-(a-c)]+[6a-(b-c)] =a-4b+c+(a-c)+6a-(b-c) =a-4b+c+a-c+6a-b+c =7a-5b+c 当a=0.1,b=0.2,c=0.3时, 原式=7×0.1-5×0.2+0.3=0; (2)∵A=2x-3y+1,B=3x+2y ∴2A-B=2(2x-3y+1)+2(3x+2y) =4x-6y+2+6x+4y =x-8y+2; (3)∵m-n=4,mn=-1 ∴(-2mn+2m+3n)-(3mn+2n-2m)-(m+4n+mn) =-2mn+2m+3n-3mn-2n+2m-m-4n-mn =-6mn+3(m-n) 当m-n=4,mn=-1时, 原式=-6×(-1)+3×4=18. |