Help converting triangular to polar

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SUMMARY

The discussion focuses on converting the equation x² + 4y² = 4 into polar coordinates. The user initially attempts to substitute x and y with their polar equivalents, leading to the equation (rcos(θ))² + 4(rsine(θ))² = 4. Through guidance, they simplify this to r²(cos²(θ) + 4sin²(θ)) = 4, ultimately recognizing that sin²(θ) + cos²(θ) = 1 can be applied, resulting in r²(1 + 3sin²(θ)) = 4. This transformation is crucial for understanding the relationship between Cartesian and polar coordinates.

PREREQUISITES
  • Understanding of polar coordinates and their relationship to Cartesian coordinates.
  • Familiarity with trigonometric identities, specifically sin²(θ) + cos²(θ) = 1.
  • Basic algebraic manipulation skills, including factoring and expanding expressions.
  • Knowledge of how to express x and y in terms of r and θ in polar coordinates.
NEXT STEPS
  • Study the derivation of polar coordinates from Cartesian coordinates.
  • Learn about the implications of trigonometric identities in coordinate transformations.
  • Practice converting various equations from Cartesian to polar coordinates.
  • Explore applications of polar coordinates in calculus, particularly in integration and area calculations.
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Students studying mathematics, particularly those in calculus or analytical geometry, as well as educators looking for examples of coordinate transformations.

dare2dream
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Homework Statement


Find an equivalent equation in polar coordinates.


Homework Equations



x^2 + 4y^2 = 4

Anyone know how to do this? I don't remember how when it's an equation...=S

My best guess is (rcos theta)^2 + 4(rsin theta)^2 = 4...but that's as far as I can get.
 
Last edited:
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how do you work out the x, y projections of a vector in the 1st quadrant? think about the unit circle and how you define sin and cos... you should be able to work out the rules that relate r and \theta to x and y.
 
I know that r^2 = x^2 + y^2 but I don't know how to use that because of the 4 in the equation. I've thought about this problem for a week and this is as far as I've gotten. -.- (This is an equation off a take-home test we received to do over spring break.)

So r^2 = x^2 + y^2, x = rcos (theta), y = rsin (theta), and tan theta = y/x

However, knowing these, I still don't get how to figure out the problem...
 
Last edited:
My best guess is (rcos theta)^2 + 4(rsin theta)^2 = 4...but that's as far as I can get.

you know the answer, so all you need is rearrange (if you want) and get r on one side while the rest on the other... I don't understand your dilemma
 
Okay...well I don't know how to do that..>.>
 
You have this (rcos theta)^2 + 4(rsin theta)^2 = 4. So expand it: r^2\cos^2\theta+4r^2\sin^2\theta=4.

Now, spot that both terms on the left contain r2, so factor this out. What do you obtain on the left hand side? Is there any way you can think of simplifying this expression you obtain?
 
So then you get r^2 (cos^2 theta + 4 sin^2 theta) = 4

I don't know how to simplify that.
 
Well, I presume you know that sin^2(x)+cos^2(x)=1. Can you use this here?
 
Yeah, I remember that, but I don't know what to do with the 4 then.
 
  • #10
4sin^2(x)=sin^2(x)+3sin^2(x)
 
  • #11
so r^2 (1 + 3sin^2 theta) = 4?
 

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