Two sides \( \Large x-3y=0\ and\ 3x+y=0 \) are perpendicular to each other. Therefore its orthocentre is the point of intersection of \( \Large x-3y=0 \) i.e. \( \Large \left(0,\ 0\right) \) so, the line \( \Large 3x-4y=0 \) passes through the orthocentre of triangle.