The point $(1,-1)$ is one of the vertices of a square. If $3 x+$ $2 y=5$ is the equation of one diagonal of the square, then what is the equation of the other diagonal?

We know that diagonal of a square bisect each other perpendicularly. Equation of a diagonal : $3 x+2 y=5$ (given). Now, equation of other diagonal that is perpendicular to the given diagonal $=2 x-3 y=K$. As vertex point $(1,-1)$ does not lies on $3 x+2 y=5$ $\{\because 3(1)+2(-1) \neq 5\}$ Then, point $(1,-1)$, must be on the diagonal $2 x-3 y=K$ Then, $2(1)-3(-1)=K$. $\therefore K=5 \text {. }$ Hence, equation of other diagonal : $2 x-3 y=5$.