if the lines `ax+by+1=0` `cx+dy+1=0` `ex+fy+1=0` are concurrent then prove that `(a,b),(c,d),(e,f) ` are collinear

The lines ax+by+c=0, bx+cy+a =0, cx+ay+b =0 are concurrent when-

If the lines ax+12y+1=0 bx+13y+1=0 and cx+14y+1=0 are concurrent then a,b,c are in

If the lines ax + y + 1 = 0, x + by + 1 = 0 and x + y + c = 0 are concurrent then prove that, (1)/( 1-a) + (1) /( 1-b) + (1) /( 1-c) = .

If the lines ax + 2y + 1 = 0, bx + 3y + 1 = 0, cx + 4y + 1 = 0 are concurrent, then a, b, c are in

If the lines ax+12y+1=0, bx+13y+1=0 and cx+14y+1=0 are concurrent, then a,b,c are in: