If the pairs of lines `x^2+2x y+a y^2=0` and `a x^2+2x y+y^2=0` have exactly one line in common, then the joint equation of the other two lines is given by `3x^2+8x y-3y^2=0` `3x^2+10 x y+3y^2=0` `y^2+2x y-3x^2=0` `x^2+2x y-3y^2=0`