2x+y=6,x-3y=1即2x-6y=27y=4，y=4/7，x=19/77y(x-3y)^2-2(3y-x)^3=7y*1^2-2(-1)^3=7y+1=5
7y(x-3y)的平方减2（3y-x)的三次方=7y(x-3y)²+2(x-3y)³=(x-3y)²(7y+2(x-3y))=7y+2x-6y=2x+y=6
