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Prove that the direction ratios of the line of intersection of two planes $\vec r\cdot(a\hat i+ b\hat j+ c\hat k)=m $ and $\vec r\cdot(d\hat i+ e\hat j+ f\hat k)=n$ is given by $\begin{vmatrix}\hat i&\hat j&\hat k\\a&b&c\\d&e&f\end{vmatrix}$ where m and n are any two real numbers.

Transforming into coordinate form, the vectors are $ax+by+cz=m$ and $dx+ey+fz=n$ .Assuming $x=t$ we can solve for $x$, $y$ and $z$ by converting into coordinate form but that method will be very long. Is there a more intuitive way to do this?

Tatai
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Hint: The line of intersection of two planes is perpendicular to the normal of each of the planes.

  • okay, how do we proceed further? – Tatai Aug 14 '21 at 08:37
  • Could anyone experienced here please tell me if I should write the answer. I was recently told that we should not answer Problem- statement questions, following which I only suggested a hint while not being sure if this is a PSQ, though the OP mentioned that she tried to solve the two equations of plane to get the equation of line! – Aman Kushwaha Aug 14 '21 at 09:26
  • @amankushwala yes lol I just realised you were talking about the cross product, no need for the answer thanks – Tatai Aug 14 '21 at 09:30