Two equal sides of an isosceles triangle are given by `7x-y+3=0` and `x+y=3`, and its third side passes through the point `(1,-10)`. Find the equation of the third side.
A. x - 3y - 7 = 0 or , 3x + y - 31 = 0
B. x - 3y - 31 = 0 or , 3x + y - 7 = 0
C. x - 3y - 31 = 0 or , 3x + y + 7 = 0
D. none of these
