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Graphing Polar Equations

Date: 06/02/2002 at 16:45:28
From: Claire
Subject: polar equation graph..very hard

Hi! 

I'm in a pre-calculus class and my teacher has assigned us to do 
these projects where we have to take a polar equation and graph it on 
a big poster board. My problem is that I don't know how to do it. 

The equation is (r-3/5)^2 = cos(7 theta). I have a feeling she made up
this equation, and no one I've asked has known how to do it, so I
would appreciate any help you'd be willing to give me. Thank you so
much.


Date: 06/02/2002 at 17:23:35
From: Doctor Ian
Subject: Re: polar equation graph..very hard

Hi Claire,

The general idea is that you choose a value for theta, figure out 
what the corresponding value of r is, and then plot the point 
(r,theta) by moving r units along the x-axis, and rotating that 
distance through theta degrees. 

Of course, this would be easier if you had something that looked 
like 

  r = [some function of theta]

wouldn't it?  So you probably want to solve the equation for r, 
to get that. Note that you're going to end up taking a square 
root... and a number always has _two_ square roots, one positive, 
and one negative.  Make sure to deal with both of them!

Does this help? 

- Doctor Ian, The Math Forum
  http://mathforum.org/dr.math/ 


Date: 06/04/2002 at 19:29:14
From: Claire
Subject: Thank you (polar equation graph..very hard)

Hey, 

Thanks for your assistance. I don't think my partner
worded our question very well... but we figured out how to
solve the equation. Our problem was that we couldn't see the
whole graph on our calculator. We asked our teacher who told
us that we can't see the whole graph so we are having fun
trying to fill it in. Thanks for the help. The +,- was key.

Thanks again, 
Drew
Associated Topics:
High School Equations, Graphs, Translations
High School Trigonometry

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