The vector equation of the plane passing through the origin  and the line of intersection of the planes r→.a→=λ and r→⋅b→=μ is

The equation of a plane through the line of intersection of the  planes r→⋅a→=λ and r→⋅b→=μ is (r→⋅a→−λ)+k(r→⋅b→−μ)=0or   r→⋅(a→+kb→)=λ+kμ--------iPutting the value of k in (i), we get the equation of the required plane as r→⋅(μa→−λb→)=0 or r→⋅(λb→−μa→)=0