x+y=960 (1+30%)x+(1+25%)y=1228 二元一次方程,

{6/x+y+10/x-y=30 6/x+y-10/x-y=-1 x>=1,x-y y=x-1(x 求导 y=[x/(1+x)]^x y'-(1/x)y=xe^-x y-x=30 y+1=3(x+1) z=0.015x*x+y*x*0.05+(1-x-y)*2.5*(x+y) x>0.35.xy>0.70x+y 1=x+y 2=20x+30y 已知x+y=a,2x-y=-2a,求[（x/y-y/x)/(x+y)-x(1/x-1/y)]/[(x+1)/y]的值 x.y都是自然数,且x(x-u)-y(y-x)+12,求x.y得值快1且x(x-y)-y(y-x)=12 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 y'/y=1/x 解方程组：x+y=xy=11 (1) x*x*y+x*y*y=30 (2) y(x+y)+(x-y)²-（x+y）（x-y）,其中x=-1/3,y=3 （x-y)(x+y)-(x+y)^2+2y(y-x),其中x=1,y=3. 2y(x+二分之一y)-[(x+y)(x-y)+2y(y+x)],其中|x-1|=2 请问60%x+20%y=30%(x+y) 怎么得到x:y=1:3 x+y＝540 （x+30）÷y＝2/1 x=?y=?