13x+11y=1392 9(x+y)=1080

{x=y-3 {x+y=11 {2x+y=13 {3x-2y=8 3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27 ｛4/(x+y)+6/(x-y)=3 ｛9/(x-y)-1/(x+y)=1 已知4x=9y求(1)x+y/y (2)y-x/2x 3x+2=y 5X+4=Y 7X+6=Y 9X+8=y 11x=y要如何计算 3x+2=y 5x+4=y 7x+6=y 9x+8=y 11x=y y-3x=2,y-5x=4,y-7x=6,y-9x=8,y-11x=0方程组, 3x+2=y 5x+4=y 7x+6=y 9x+8=y 11x=y 联立方程 有的话 解方程组: ｛3x+2y=13 3x-2y=5 ｛x-y/3=x+y/2+1 2x-5y=9 二元函数f(x,y)=x+y/x-y,求f(y/x,x/y) ｛2x-5y=21,{2x+y=6 {x-3y=1 {y=-2x+3 y=-x; y=1/2x+1 5x-9y=-13 [x(x-y)-y(x-y)+(x+y)(x-y)]÷2x其中x=2012 y=2013