Calculating Direction Cosines for Linear Equations - Homework Help

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In summary, the conversation is about finding the direction cosine of a given equation (4x+5y+7z=13) and the confusion over whether it is an equation for a line or a plane. The direction cosines of a line in three dimensions are the cosines of the angles the line makes with the three coordinate axes, and are calculated using a unit vector in the direction of the line.
  • #1
Rahul Manavalan
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Homework Statement


To find the direction cosine of a equation say (4x+5y+7z=13)

Homework Equations



Im not really sure what to do

The Attempt at a Solution


(I know this is really basic but i would be glad if someone helps me with this
 
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  • #2
Rahul Manavalan said:

Homework Statement


To find the direction cosine of a equation say (4x+5y+7z=13)

Homework Equations



Im not really sure what to do

The Attempt at a Solution


(I know this is really basic but i would be glad if someone helps me with this
Is that the complete question?

What have you tried? Where are you stuck ?

What is that the equation of?

How can such an object have direction cosines?
 
  • #3
Rahul Manavalan said:

Homework Statement


To find the direction cosine of a equation say (4x+5y+7z=13)

Homework Equations



Im not really sure what to do

The Attempt at a Solution


(I know this is really basic but i would be glad if someone helps me with this
Looks like the equation for a plane. How do you usually find a normal to a plane?
 
  • #4
The problem appears to be that the OP really does NOT understand the basics of three dimensional lines. Rahul, as SteamKing said, the equation you give defines a plane in three dimensions, not a line. The "direction cosines" of a line in three dimensions are the cosines of the angles the line makes with lines parallel to the three coordinate axes. In addition, They are the dot products of a unit vector in the direction of the line with unit vectors in the directions of the three coordinate axes. In particular, if a line is given in parametric form, x= at+ b, y= ct+ d, z= et+ f, then the vector ai+ bj+ ck is in the direction of the line. Dividing by [itex]\sqrt{a^2+ b^2+ c^2}[/itex] is gives a unit vector in that direction. In other words, the three direction cosines are [itex]\frac{a}{\sqrt{a^2+ b^2+ c^2}}[/itex], [itex]\frac{b}{\sqrt{a^2+ b^2+ c^2}}[/itex], and [itex]\frac{c}{\sqrt{a^2+ b^2+ c^2}}[/itex].
 

Related to Calculating Direction Cosines for Linear Equations - Homework Help

1. How do I calculate direction cosines for linear equations?

To calculate direction cosines for linear equations, you first need to find the dot product of the given vector and the unit vector. Then, divide the result by the magnitude of the given vector to get the direction cosine. Repeat this process for each component of the vector to get the direction cosines for all three dimensions.

2. Why do we use direction cosines in linear equations?

Direction cosines are used in linear equations to represent the direction of a vector in three-dimensional space. They provide a way to express the orientation of a vector without having to use angles, which can be difficult to visualize and work with in higher dimensions.

3. How do I find the magnitude of a vector for calculating direction cosines?

The magnitude of a vector can be found by taking the square root of the sum of the squares of its components. This can also be written as the square root of the dot product of the vector with itself.

4. Can direction cosines be negative?

Yes, direction cosines can be negative. The direction cosines represent the cosine of the angle between the vector and the unit vector in each dimension. Since the cosine function can have positive or negative values, direction cosines can also have positive or negative values.

5. How do I use direction cosines to find the angle between two vectors?

To find the angle between two vectors, you can use the dot product formula: cosθ = (u.v) / (|u||v|), where u and v are the two vectors and |u| and |v| are their magnitudes. Once you have the cosine of the angle, you can use inverse cosine (cos^-1) to find the angle in radians or degrees.

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