Find perpendicular vector and plane through given point

theown1
Messages
12
Reaction score
0

Homework Statement


Consider the line and plane below.
x = 5-5t, y = 3+7t, z = 10t
ax + by + cz = d

Find values of a, b, c, and d so that the plane is perpendicular to the line and through the point (2, 1, 2).

Homework Equations


Fgrad=(x',y',z') is perp to surface
if \vec{v}1\bullet\vec{v}2=0
then v1\botv2

The Attempt at a Solution



when I put those x,y,z values together I get a parametric equation that equals <5,3,0>+t<-5,7,10>

the starting point <5,3,0> I think is not relevant to finding a perpendicular vector,
I just need to find a vector perpendicular to t<-5,7,10> that goes through (2,1,2) i think? but I'm not sure how to do this..
then once I find the vector that's perp to t<-5,7,10>(dot)<a,b,c>=0
once I know a,b,c I can solve for d
 
Physics news on Phys.org
Consider the equation of the line:
(x,y,z) = (5,3,0) + t(-5,7,10)
Which is really just translated from:
(x,y,z) = t(-5,7,10)
Which is what you have so far.
So by definition the plane is defined by all vectors perpendicular to (-5,7,10)
Which is just 7y + 10z - 5x = 0
Translated plane:
v dot (x-x0) = 0
You complete.
 
theown1 said:

Homework Statement


Consider the line and plane below.
x = 5-5t, y = 3+7t, z = 10t
ax + by + cz = d

Find values of a, b, c, and d so that the plane is perpendicular to the line and through the point (2, 1, 2).

Homework Equations


Fgrad=(x',y',z') is perp to surface
if \vec{v}1\bullet\vec{v}2=0
then v1\botv2


The Attempt at a Solution



when I put those x,y,z values together I get a parametric equation that equals <5,3,0>+t<-5,7,10>

the starting point <5,3,0> I think is not relevant to finding a perpendicular vector,
I just need to find a vector perpendicular to t<-5,7,10> that goes through (2,1,2) i think?
No, you don't. You want to find a vector perpendicular to the plane in order to write the equation of the plane. Since the line itself is perpendicular to the plane, its "direction vector", <-5, 7, 10>, is perpendicular to the plane.
So you know the plane can be written as -5(x-x_0)+ 7(y-y_0)+ 10(z-z)= 0, where (x_0, y_0, z_0) is some point in the plane. Any you are also given that.&lt;br /&gt; &lt;br /&gt; &lt;blockquote data-attributes=&quot;&quot; data-quote=&quot;&quot; data-source=&quot;&quot; class=&quot;bbCodeBlock bbCodeBlock--expandable bbCodeBlock--quote js-expandWatch&quot;&gt; &lt;div class=&quot;bbCodeBlock-content&quot;&gt; &lt;div class=&quot;bbCodeBlock-expandContent js-expandContent &quot;&gt; but I&amp;#039;m not sure how to do this..&lt;br /&gt; then once I find the vector that&amp;#039;s perp to t&amp;lt;-5,7,10&amp;gt;(dot)&amp;lt;a,b,c&amp;gt;=0&lt;br /&gt; once I know a,b,c I can solve for d &lt;/div&gt; &lt;/div&gt; &lt;/blockquote&gt;
 
Ok, ok I understand now

since the line is already perp. to the plane, the direction of the line corresponds to the gradient of the plane which is <a,b,c> and then i just use the equation of a plane to solve
d=a(x-xo)+b(y-yo)+c(z-zo)

thanks
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top