求(1)y=x*(5-2x) ,(2)y=x^2*(5-2x) ,(3)y=x*(5-2x)^2 的最大值,x全属於(0,5/2)

(x-y)/(x+y)=3求( 3x-2y-1)/(x+y-5) {(x+y)/2+(x-y)/3=1,(x+y)-5(x-y)=2.求x=?,y=? 已知x-y/x+y=3,求代数式5(x-y)/x+y-x+y/2(x-y) x+2y=2x+y+1=7x-y 求：2x-y? 求(X+Y)(X-Y)(X²+Y²),X=5 Y=2, 若x*x+y*y=x+y-1/2,求x,y的值如题 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 若2/x-1/y=3,求[y/x-y/x-y(x-y/x-x+y)]/x-2y/x的值 x^2-x+y^2+2y+5/4=0 求x^-1+y^0 4x-3y=5 x^2+y^2=1 求x,y 3x+4y-5=0 x^2+y^2=1求x.y x+y=8 2x-y=1 求3x+5y 已知x>0,y>0,2/x+5/y=1,求x+y最小值 已知:2x-y/x+y=1/5,求2x+5y/6x-2y的值 已知x+y=-1,xy=-2,求代数式-5（x+y)+(x-y)+x(xy+y)的值 若(x*x+y*y)(x*x+y*y)-4x*x*y*y=0,求代数式(x*x+5xy+y*y)/(x*x+2xy+y*y)的值 x+y=1,xy=-1/2,求x(x+y)(x-y)-x(x+y)2 1.y=x^5+5^x+x^x+lgx 2.y=xe^x^2求y'' 3.已知y=e^f(x),则y''= 4.已知y=(1+x)^x,求导数y'