Q.

The equation of the line passing through the origin and the point of intersection of the lines xa+yb=1 and xb+ya=1 is

1 bx-ay=0  
2 x+y=0   
3 ax-by=0  
4 x-y=0  

Ans.

(4)

Given equation of lines are

xa+yb=1,    xb+ya=1

or    bx+ay=ab                          ...(i)

       ax+by=ab                          ...(ii)

Solving (i) and (ii),

         x=aba+b,    y=aba+b

So equation of line passing through (0,0) is

y-0=aba+baba+b(x-0)⇒y=x