If a variable line drawn through the intersection of the lines $\large\frac{x}{3}+\frac{y}{4}$$=1$ and $\large\frac{x}{4}+\frac{y}{3}$$=1$ , meets the coordinate axes at $A$ and $B,(A \neq B),$ then the locus of the midpoint of AB is :

Question

$\begin{array}{1 1} (1) 6xy=7(x+y) \\ (2) 4(x+y)2−28(x+y)+49=0 \\ (3) 7xy=6(x+y) \\ (4) 14(x+y)2−97(x+y)+168=0 \end{array} $