A line is drawn through the point $(1,2)$ to meet the coordinate axes at $P$ and $Q$ such that it forms a triangle of area $\frac{9}{2}$ sq. units with the coordinate axes. The equation of the line $PQ$ is\\
(1) $x+2y=5$\\
(2) $3x+y=5$\\
(3) $x+2y=4$\\
(4) $2x+y=4$