1.=> mx-m=-nx+2n+2007 => (m+n)x =m+2n+2007无数个解 => m+n=0; m+2n+2007=0
不用求出m,n =>m^2007 +n^2007=(-n)^2007+n^2007=-n^2007+n^2007 =0...ans
2.=> 260=So +5v ; 340=So+7v => So=60;v=40 => S=60+1.5*40=120...ans
3.单价甲x、乙y、丙z => 5x+2y+4z=80 ; 3x+6y+4z=144相加8x+8y+8z=224
=>x+y+z=28...ans