{y=x+3,7x+5y=9 {y=2x-7,5x+3y2z
{3s-t=5,5s+2t=15
{3x+4y=16,5x-6y=33
{4(x-y-1)=3(1-y)-2,二分之一x加上三分之一y=2
{3u+2t=7,6u-2t=11
{2a+b=3,3a+b=4
{2x-5y=-3,-4x+y=-3
{二分之一x-二分之三y=-1,2x+y=3