设x*y=xy+x-y,如3*6=3×6+3-6=15,若a*2=7,2*b=9求(1)a-b的值(2)a*b的值

设x=【1/3】y,求【3y/x+3y】+【x/3y-x】-【6xy/9y²-x²】的值. 设x,y>=0,2x+y=6,求z=4x^2+3xy+y^2-6x-3y的范围 设实数x,y适合等式x*2-4xy+4y^2+√3x+√3y-6=0,则x+y的最大值是, 设xy>=0,2x+y=6,求z=4x^2+3xy+y^2-6x-3y的最值 已知xy=-2,x-y=3,求（x+y)（x-y)-y^2+（x-y)^2-（6x^2y-2xy^2)÷2y 已知xy/x+y=6,求3x-2xy+3y/-x+3xy-y的值. 已知(xy)/(x+y)=6求(3x-2xy+3y)/(-x+3xy-y)的值. 诺x+y=6,xy=4 求(5x-4y-3xy)-(8x-y+2xy) 已知x-y=3xy,且xy不等于0,则-3x+6xy+3y/(7x-5y)-9xy-(3x-y) x^+2xy+y^+4=16 x^-2xy+y^=16 求(3xy+6y^)+|x^-(2xy+2y^-3x^)|的值 化简求值x-4y/2x-7xy+3y×x-2xy-3y/2x+3xy-2y÷3x-6y/4x-4xy+y,其中：x=1999,y=-1 已知:x/y=-2,求x^2-2xy-3y^2/x^-6xy 2(x*x-3xy-2y*y+2)- =-4y*y-6xy+3x 已知x y=6,xy=-3,则3x-2xy 3y的值等于?如题补充：是已知x+ y=6,xy=-3,则3x-2xy +3y的值等于? 几道微积分题求解下列微分方程1.xy'=y ln（y/x）2.xy‘-y=x tan（y/x）3.xy’+y=x^2+3x+24.(y^2-6x)y'+2y=05.xy'-[1/(1+x)]y=x,y(x=1)=16.设f(x)-(微分符号下面0上面x)f(t)dt=x,求f(x) 设xy满足约束条件,1≤x,x+y≥2,y≥3x-6,则z=2x+y最小值 设xy属于R,且X平方/6+Y平方/3=1,求x+y的最小值 设变量xy满足约束条件x-y≥0,x+y-2≥0,3x-y-6≤0则目标函数z=2x-y设变量xy满足约束条件x-y≥0,x+y-2≥0,3x-y-6≤0则目标函数z=2x-y的最小值为（ ）.