1.-x+4y=9(1)

｛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 9y=3x-(x-1),4(x+y)-(2x+4)=8y 1.-x+4y=9(1) 解方程组{4/x+y+6/x-y=3, 9/x-y-1/x+y=1 解方程组：{4/x+y+6/x-y=3 9/x-y-1/x+y=1} x>0 y>0 x+y=1,4/X+9/y最小值 化简(x+y)+(2x+1/2y)+(3x+2/3y)+(4x+3/4y)+...+(9x+8/9y)=? 化简求值：(7x-2y)(3x-2y-1)-(4x+3y)(9x+6y),其中x=2,y=-1 已知集合M={(x,y)|x,y为实数,且x²/4-y²/9=1},N {(x,y)|x,y为实数, 1.已知1/x+1/y=-1/x+y,则y/x+x/y=? {3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1