(1)-49/y^2+16/x^2=(2)48-3t^2=(3)x-14x+49=(4)a-6a^2b^3+9a^3b^5=(5)(a^2+b^2)-4a^2b^2=

x-y/x-x+y/y-(x+y)(x-y)/y² y/x=2 若x-y=1 化简（x+y)(x^2+y^2)(x^4+y^4)(x^8+y^8)(x^16+y^16) 2y(x+二分之一y)-[(x+y)(x-y)+2y(y+x)],其中|x-1|=2 （x-y)(x+y)-(x+y)^2+2y(y-x),其中x=1,y=3. 4x+2y=16 x-y=1, 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 2(x-y)/3-(x+y)/4=-1 (1) 6(x+y)-4(2x-y)=16 (2) （x-4y=-1 2x+y=16) (x-y=1 2x+y=5 ) (2x-2y)/3-(x-y)=-1和6(x+y)-4(2x-y)=16 解方程组2(x-y)/3-x+y/4=-1 6(x-y)-4(2x-y)=16 解方程组：2(x-y)/3-x+y/4=-1 ,6(x+y)-4(2x-y)=16 3分之2(X-Y)-4分之X+Y=-1,3(X+Y)-2(X-Y)=16 2(X-Y)/3=(X+Y)/4 -1 6(X+Y)=4(2X-Y)+16解方程 6(x+y)=4(2x-y)+16,2(x-y)/3=x+y/4-1 2(x-y)/3—x+y/4=1 6(x+y)—4(2x-y)=16 3分之2(x-y)-4分之x+y=-1 8(x+y)-4(2x-y)=16 x+2y=2x+y+1=7x-y 求：2x-y?