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Find equation of a plane that passes through point P $(-1,4,2)$ that contains the intersection line of the planes $\begin{align*} 4x-y+z-2&=0\\ 2x+y-2z-3&=0 \end{align*}$

Attempt: I found the the direction vector of the intersection line by taking the cross product of vectors normal to the known planes. I got $\langle 1,10,6\rangle$. Now, I need to find a vector normal to the plane I am looking for. To do that I need one more point on that plane. So how do I proceed?

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    The direction vector alone does not suffice: You need to find a point that lies on the intersection line. Of course, this point also lies in the plane you are looking for.2012-04-27

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Put the two given equations together in a system, set $x=0$ (say) and solve for $y,z$ to get an actual point on the intersection line. Accompanied by its direction vector and the outlying point $P$, we can determine three points from the desired plane and subsequently determine an equation for it.


Dostre's edit (see comments)

$x=0:\begin{cases} y-2z-3=0 \\ -y+z-2=0 \end{cases}$ ;$\;\;\;\;$ add them up and you get:

$\;\;\;\;\;\;\;\;\;\;\begin{cases} -z-5,\;\;z=-5\\ -y+z-2=0,\;y=-7 \end{cases}\Rightarrow$Point $ (0,-7,-5)$, call it Q, is on the line of intersection.

So now we have two points $P(-1,4,2)$ and $Q(0,-7,-5)$ on our desired plane and vector w thats is parallel to the desired plane. In order to find the equation of the desired plane we need a vector that is normal to it.We can find that normal vector by taking cross product of two vectors that are parallel to the desired plane. We already have w so the other vector will be

*PQ*$<0-(-1),-7-4,-5-2>=<1,-11,-7>$

Now normal vector to desired plane will be the cross product of w and PQ:

PQ x w=$\begin{vmatrix} i & j & k \\ 1 & -11 & -7 \\ 1 & 10 & 6 \end{vmatrix}=i\begin{vmatrix} -11 & -7 \\ 10 & 6 \end{vmatrix}-j\begin{vmatrix} 1 & -7 \\ 1 & 6 \end{vmatrix}+k\begin{vmatrix} 1 & -11\\ 1 & 10 \end{vmatrix}=4i-13j+21k$

$4i-13j+21k=<4,-13,21>$ is the vector normal to the desired plane.

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    @Dostre: Ah, of course it's -13, and yes I meant $x=0$. :-) Go ahead and edit, I don't mind.2012-04-27
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Consider the family of planes $u(4x-y+z-2)+(1-u)(2x+y-2z-3)=0$ where $u$ is a parameter. You can find the appropriate value of $u$ by substituting in the coordinates of the given point and solving for $u$; the value thus obtained can be substituted in the equation for the family to yield the particular member you need.

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    Ok I substituted $u=\frac{-5}{3}$ into the equation and it worked out. Just needed to pay attention to the arithmetic. After multiplying out everything I got $\frac{-4}{3} x+\frac{13}{3} y-\frac{21}{3} z -\frac{14}{3}=0$. To make it look like the answer in my textbook I just had to multiply both sides by $-3$. Thanks. Your method is useful. Sorry about the comment edit.2012-04-28
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Find any point that belongs to the line by looking for the intersections of this line with the coordinate planes. E.g., put $z=0$ and find $x$ and $y$ from the system $ 4x-y=2,\quad 2x+4=3. $

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    Thanks Artem. Now I got the idea2012-04-27