John's question at Yahoo Answers (parametric equations of a line).

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Thus, solving the first equation for $y$ gives $y=-\dfrac{1}{8}-\dfrac{7}{8}t$, hence substituting it into the second equation we get$-9t-\dfrac{7}{8}t+4z=-7\;\Rightarrow\;z=-\dfrac{63}{32}+23t$Finally, $r\equiv\left \{ \begin{matrix}x=t\\y=-\dfrac{1}{8}-\dfrac{7}{8}t\\z=-\dfrac{63}{32}+23t\end{matrix}\right.\quad (t\in\mathbb{R})$
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Fernando Revilla
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Here is the question:

Find parametric equations of the line of intersection of the two planes 7x+8y = -1 and -9x-7y+4z = -7.
What is the direction vector used?

Here is a link to the question:

Calculus III Intersecting Planes? - Yahoo! Answers

I have posted a link there to this topic so the OP can find my response.
 
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  • #2
Hello John,

A direction vector of the intersection line $r$ is

$v=(7,8,0)\times (-9,-7,4)=\det \;\begin{bmatrix}{i}&{j}&{k}\\{7}&{8}&{0}\\{-9}&{-7}&{4}\end{bmatrix}=(32,-28,23)$

For $x=0$ we get the system $8y=-1,\;-7y+4z=-7$ which implies $y=-1/8$ and $z=-63/32$. Hence,

$r\equiv\left \{ \begin{matrix}x=32t\\y=-\dfrac{1}{8}-28t\\z=-\dfrac{63}{32}+23t\end{matrix}\right.\quad (t\in\mathbb{R})$Another way is to solve the system:

$\left \{ \begin{matrix}7x+8y = -1\\-9x-7y+4z = -7\end{matrix}\right.$

as a function (for example) of $x=t$.
 

Related to John's question at Yahoo Answers (parametric equations of a line).

1. What are parametric equations of a line?

Parametric equations of a line are a way of representing a line in two-dimensional space using two variables, typically denoted as x and y. These equations express the coordinates of any point on the line as functions of a third variable, usually denoted as t.

2. How are parametric equations of a line different from slope-intercept form?

Parametric equations use a third variable to represent the coordinates of points on a line, while slope-intercept form uses the slope and y-intercept of a line. Parametric equations are also more flexible and can represent lines in any orientation, while slope-intercept form is limited to lines that are either horizontal or vertical.

3. How do you convert parametric equations of a line to slope-intercept form?

To convert parametric equations to slope-intercept form, you can eliminate the third variable by solving for t in terms of x or y. This will give you an equation in the form y = mx + b, where m is the slope and b is the y-intercept.

4. What are some real-world applications of parametric equations of a line?

Parametric equations are used in many fields, including physics, engineering, and computer graphics. They are often used to model the motion of objects in space, such as the trajectory of a projectile, or the position of a point on a moving object. They are also used in computer graphics to create smooth and realistic animations.

5. How do you graph parametric equations of a line?

To graph parametric equations, you can first choose a range of values for the third variable, t. Then, plug these values into the parametric equations to find the corresponding x and y coordinates. Plot these points on a graph and connect them to create the line. Alternatively, you can use a graphing calculator or online graphing tool to automatically plot the line for you.

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