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#1 2017-03-07 18:52:05
- davidtrinh
- Member
- Registered: 2016-12-03
- Posts: 10
I can't find the third answer in the polar equations.
I am going to write down a problem below.
(ex) Find the points of intersection of r=1-sin(u) and r=1+sin(u) without drawing their graphs.
This is how I do it.
I equate the two equations and get 1-sin(u)=1+sin(u). Simplifying it gives
sin(u)=0. Solving for u gives 0 and pi. Then, the two points are (1 , pi) and (1 , 0).
They are correct. The answer key gives one more answer (0 , pi/2).
How do you find the third answer without graphing? Thanks for your help.
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#3 2017-03-08 08:00:39
- anonimnystefy
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- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: I can't find the third answer in the polar equations.
So, another equation that would give you a solution would be
Last edited by anonimnystefy (2017-03-08 08:04:41)
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#4 2017-03-08 19:47:02
- thickhead
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- Registered: 2016-04-16
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Re: I can't find the third answer in the polar equations.
In polar coordinates r is always positive.
{1}Vasudhaiva Kutumakam.{The whole Universe is a family.}
(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha
{Gods rejoice at those places where ladies are respected.}
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#5 2017-03-09 04:00:28
- anonimnystefy
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- From: Harlan's World
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Re: I can't find the third answer in the polar equations.
Except not really.
Here's a link relevant to the original post: Intersection of polar curves
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#6 2017-03-09 04:41:32
- Bob
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- Registered: 2010-06-20
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Re: I can't find the third answer in the polar equations.
Actually, there is another solution, since in polar coordinates the point is the same one as the point
So, another equation that would give you a solution would be
.
Great to hear from you again!!!
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob 
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#7 2017-03-09 05:26:19
- anonimnystefy
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- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: I can't find the third answer in the polar equations.
Hi Bob!
How've you been?
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#8 2017-03-09 06:10:04
- Bob
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Re: I can't find the third answer in the polar equations.
hi Stefy,
I think my brain is still functioning.
How about you? Uni beckoning?
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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#9 2017-03-09 12:28:34
- anonimnystefy
- Real Member
- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,049
Re: I can't find the third answer in the polar equations.
Good to know! x)
Yeah, I've been a been lacking in the uni department lately, because I got a temporary job, so I had less time to study, but it's pretty good otherwise! 
Here lies the reader who will never open this book. He is forever dead.
Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.
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#10 2017-03-09 20:12:53
- Bob
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- Registered: 2010-06-20
- Posts: 10,619
Re: I can't find the third answer in the polar equations.
Don't know why I didn't do this earlier:
Clearly three (not two) solutions.
Bob
Children are not defined by school ...........The Fonz
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you! …………….Bob
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