第一部分1. 4x+y-z=123x+2y+z=-5x-y+5z=12. 2a+7b=33a-c=1-b+3c=43. x:y=3:2y:Z=5:4x+y+z=664. a-d=-4d-2y=-1a+s-d=-15. a=6sa-4=10s-20da+12=3y+18d6. a+s=8a+d=6s+d=107. 3(a+s-d)=15(d-a...