Giving the Equation of a Line in terms of X, y and theta

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Discussion Overview

The discussion revolves around defining the equation of a line in terms of variables x, y, and theta within Mathematica, particularly in the context of finding the intersection of this line with a circle. The problem is framed around a lighthouse beam rotating over a circular island, and participants explore various mathematical representations and approaches to solve the problem.

Discussion Character

  • Exploratory
  • Technical explanation
  • Homework-related

Main Points Raised

  • One participant proposes using the relationship tan(θ) = y/x to express the line as y = (7/3)tan(θ) for finding intersections with the circle.
  • Another participant provides Mathematica code to reduce the equations for the line and circle, yielding specific intersection points.
  • A later reply questions the clarity of the original problem and suggests that the initial guess may be incorrect.
  • One participant clarifies the context of the problem, detailing the lighthouse scenario and the need to derive several equations related to the beam's rotation.
  • Another participant suggests using y = xtan(θ) to represent the line, questioning if this forms a radial line from the center.
  • There is a mention of the beam's angular velocity and its implications on the distance between entry and exit points on the island.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the problem statement, with some uncertainty about the initial conditions and assumptions. Multiple approaches to defining the line and calculating intersections are presented, indicating that no consensus has been reached on the best method.

Contextual Notes

Participants note the complexity of the problem, which involves multiple parts and requires careful consideration of the beam's rotation and its effects on the distances involved. There are unresolved aspects regarding the definitions and assumptions made in the problem.

MohammedKhan
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Given an equation for a line y=7x/3, how can i define it in mathematica using x,y and theta.
I am eventually going to have to find the intersection of this line to a circle with the equation Circle[{0,9},5] as a function of theta.

I thought maybe if i use the rule tan(θ) = y/x then id get something along the lines of y = (7/3)tanθ, but then I don't know how to define this in mathematicas language.
 
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In[1]:= Reduce[{y==7x/3,x^2+(y-9)^2==5^2},{x, y}, Backsubstitution->True]

Out[1]= (x==(189-3*Sqrt[721])/58 && y==(441-7*Sqrt[721])/58) || (x == (189+3*Sqrt[721])/58 && y == (441+7*Sqrt[721])/58)

In[2]:= N[Reduce[{y==7x/3,x^2+(y-9)^2==5^2},{x,y},Backsubstitution->True]]

Out[2]= (x==1.86975&&y==4.36276)||(x==4.64749&&y==10.8441)
 
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in the question however it states that the beam passes through the circle as function of theta. so can i say this in addition to wat you wrote.

In[1]:= Reduce[{y==(7x/3)Tan[θ],x^2+(y-9)^2==5^2},{x, y}, Backsubstitution->True]

would this now solve for the intersection as a function of theta?
 
I do not understand what the question is, but I assume your guess is incorrect.
 
MohammedKhan said:
Given an equation for a line y=7x/3, how can i define it in mathematica using x,y and theta.
I am eventually going to have to find the intersection of this line to a circle with the equation Circle[{0,9},5] as a function of theta.

Is this a homework problem?
Is the problem stated exactly as you have said?
Is the problem stated in English?
Is there any perhaps simpler previous example problem with a solution available?

If you can provide all that then perhaps we can find a solution for you.
 
ok so here's the question

A lighthouse is located 9 miles south of the center from the center of a circular island of diameter 10 miles in d.When the beam is over the island the beam enters at a point on the shore and leaves at another point,. As the beam rotates the distance between these two points changes.

The beam is making 3 revolutions per minute clockwise.

At what rate is the the distance between the two points changing when the beam enters 3miles east of the line between the lighthose and the center of the island.

its divided into a few parts.

1. Give the equation for the beam it should be in terms x,y and tan(\[Theta]). Name it eqbeam.

2. Find the line segment between the entrance and the exit point as a function of \[Theta]. Name it lineseg

3. Give the derivative of the distance between the two points with repect to \[Theta]

4. What is the angular velocity of the beam?

5. What are the coordinates of the entry point three miles east of the line between the light house and the center of the island.

6. At what rate is the the distance between the two points changing when the beam enters 3 miles east of the line between the lighthose and the center of the island.ok the tan(theta) thing i suggested def didnt make sense i was just guessing. I am thinkin how can you make a formula that accounts for the beam rotating clockwise. i would assume the dtheta/dt = 6pi per minute. i was thinkin along the lines of (x',y') = ((xcostheta - ysintheta),(xcostheta + ysintheta)) for two arbitrary points and then using getting a line from that?
 
ok so i used tan[theta] = y/x to get y =xtan[theta] for the equation of the line. i think it worked out. does that make sense tho? does that form a radial line originating from the center.
 

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