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#1 2006-08-11 13:11:41

fusilli_jerry89
Member
Registered: 2006-06-23
Posts: 86

Simple Trig

On a math test, the question was as follows: If Cosθ = -5/13 and θ is in quadrant 2, determine Cotθ. I got  -5/12, but the teacher circled 5/12 as the right answer.

Last edited by fusilli_jerry89 (2006-08-11 23:12:14)

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#2 2006-08-11 13:33:29

Ricky
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Registered: 2005-12-04
Posts: 3,791

Re: Simple Trig

If theta is is quadrant II, the cosine is negative and sine is positive.  Thus, tanget is negative and so cotangent must be negative.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#3 2006-08-11 13:38:08

fusilli_jerry89
Member
Registered: 2006-06-23
Posts: 86

Re: Simple Trig

Ricky wrote:

If theta is is quadrant II, the cosine is negative and sine is positive.  Thus, tanget is negative and so cotangent must be negative.

So your saying that you take the answer I got which is -5/12 and add another negative since in quadrant 2, tan is negative, and you get 5/12?

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#4 2006-08-11 15:12:01

Ricky
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Registered: 2005-12-04
Posts: 3,791

Re: Simple Trig

No, I'm saying that cotangent of an angle in the 2nd quadrant must be negative.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#5 2006-08-11 23:11:54

fusilli_jerry89
Member
Registered: 2006-06-23
Posts: 86

Re: Simple Trig

Ricky wrote:

No, I'm saying that cotangent of an angle in the 2nd quadrant must be negative.

well my answer was negative, but the teacher circled the positive one...

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#6 2006-08-12 03:52:38

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

Re: Simple Trig

Which would mean your teacher is wrong.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#7 2006-08-12 08:59:51

fusilli_jerry89
Member
Registered: 2006-06-23
Posts: 86

Re: Simple Trig

k well thanks then

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