The third side is parallel to a bisector of the angle between equal sides. The bisectors are 7x−y+3=±5(x+y−3) ⇒2x−6y+18=0 or 12x+4y−12=0 ⇒x−3y+9=0 or 3x+y−3=0 Let the third side be x−3y=k or 3x+y=L It passes through (1,−10). k=31,L=−7 Hence, required lines are x−3y=31,3x+y=−7