x/4+y/4=2.25;x/2-y/12=1.75. 怎么解啊?

{3(x+y)-4(x-y)=4 {x+y/2 + x-y/6=1 x+y+2(-x-y+1)=3(1-y-x)-4-(y+x-1),x+y=? 已知:【(x²+y²)-(x-y)²+2y(x-y)】/4y=1,求4x/4x²-y²-1/2x+y 先化简 再求值 (2x-y)(y+x)-(x-2y)(2y+x)-(-3y+x)^2其(√x+1)+y^2+4=-4y 化简[(3x+4y)^2-(2x+y)(2x-y)+(-x+y)(5x-y)]除以-2y,其中x=-1,y=1 已知x-y=1,求[(x+2y)^2+(2x+y)(x-4y)-3(x+y)(x-y)]除以y的值大神们帮帮忙 已知x-y=1,求[(x+2y)²+(2x+y)(x-4y)-3(x+y)(x-y)]÷y的值 (x-y) (x-2y)+(x+2y) (x-3y)-2(x-3y) (x-4y)= (x-4y)(2x+y)= [(y-2x)(-2x-y)-4(x-2y)²]*2y,其中x=1,y=2 [(x+y)(x-y)-(x-y)^2-4xy]/2y,其中x=1,y=-1 [(y-2x)(-2x-y)+4(x-2y)平方]/3y,其中x=1,y=-3 (x+y)(x-y)+4(y-1) [(2x+y)^2+(y+2x)(y-2x)-2y(4x-y)]/4y,其中x=1/2,y=1/3 x²/xy-x/y 3x/4x+y - x-2y/4x+y (1-y/y+x)÷x/y²-x² 先化简,再求值：[(x+y)(x-y)-(x-y)^2+2y(x-3y)]/(-4y),其中x=1,y=-2 先化简,再求值:[(x＋y)(x-y)-(x-y)²+2y(x+y)]除4y,其中x=2,y=1 9y=3x-(x-1),4(x+y)-(2x+4)=8y