化简:6(0.9y-x)=9(y-30-x)

｛4/(x+y)+6/(x-y)=3 ｛9/(x-y)-1/(x+y)=1 化简：x-y/x+3y÷x^-y^2/x^2+6xy+9y^2-(xy/x+y) (x-y)³+9(x-y)-6(x-y)² 化简,求值:[(x-2y)^2+(x-2y)(x+2y)-2x(2x-y)]/2x,其中x=5.y=-6 化简:x-y/x+3y÷x^2-y^2/x^2+6xy+9y^2-2y/x+y x+y=20-6 3x+y=30 X+Y=9 6X+7Y=59 x+y=3 x+2y=9 3/x+1=y y-x=3 y=2x-3 y-3x=1 2(x+1)-y=6 7x-5y=-9 【2(x-y)^3-8(x-y)^2(x+y)+6y(x-y)^2】/2(x-y)^2= 已知方程组2x+y=6,x+2y=9,则x+y=() x-y=() ? 已知6x+2y/9x-3y=6,那么(3x+y)平方/x平方-y平方 已知方程组{2x+y=6 x+2y=9},求x+y与x-y的值