3^x=212^y=8=2^3=(3^x)^3=3^3x 12^y=(3*4)^y=(3^y)*[(2^2)^y]=(3^y) * (2^2y)=(3^y) * (3^x)^2y=(3^y)*(3^2xy)=3^(y+2xy)=3^3x所以 y+2xy=3xy-3x=-2xy1/x - 3/y=(y-3x)/xy = -2xy/xy=-2