The third side of the isosceles triangle is parallel to the angle bisector of the given lines 7x−y+3=0 and x+y−3=0 Now, the equation of angle bisectors are
7x−y+3
√50
=±
x+y−3
√2
⇒7x−y+3=±5(x+y−3) or 2x−6y+18=0 and 12x+4y−12=0 or x−3y+9=0 and 3x+y−3=0 Therefore, possible equation of third side passes through point (2,−5) are x−3y=17 or 3x+y=1