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June 14th, 2010, 06:49 PM  #1 
Member Joined: Jun 2010 From: USA, Texas Posts: 85 Thanks: 0  [TRIG] Indentities
I need help with some unlisted identities. Like for example: (secx) (secx) = sec^2x = 2secx ?? (cscx  1) (cscx + 1) = ? (1  cosx)  (1 + cosx) = ? (secx + tanx) + (secx  tanx) = ? 
June 14th, 2010, 07:11 PM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,941 Thanks: 2210 
They seem straightforward; can you explain why they are troubling you?

June 14th, 2010, 07:22 PM  #3 
Member Joined: Jun 2010 From: USA, Texas Posts: 85 Thanks: 0  Re: [TRIG] Indentities
I just don't understand what to do when I come into those situations. Like I don't understand how/why (cscx1) (cscx+1) = (1/sinx)  (1/1) And the others listed in 1st post. 
June 15th, 2010, 02:01 AM  #4  
Member Joined: Jun 2010 Posts: 44 Thanks: 0  Re: [TRIG] Indentities Quote:
 
June 15th, 2010, 04:20 AM  #5 
Member Joined: Jun 2010 From: USA, Texas Posts: 85 Thanks: 0  Re: [TRIG] Indentities
So what I'm asking is what does it equal then?

June 15th, 2010, 06:02 AM  #6 
Global Moderator Joined: Dec 2006 Posts: 20,941 Thanks: 2210 
You need to find the total of the (four in this case) products of each term within the first pair of parentheses and each term within the second pair of parentheses: (csc(x)  1)(csc(x) + 1) = csc²(x) + csc(x)  csc(x)  1 = csc²(x)  1. The result simplifies further to cot²(x), since there is a standard identity (corresponding to Pythagoras) that tells you that cot²(x) + 1 = csc²(x). The last two of your original examples didn't involve multiplication; you just needed to be able to add and subtract. Why were those causing difficulty for you? Are you perhaps tackling trigonometry without taking the trouble to revise the basics of arithmetic, algebra and geometry first? 
June 15th, 2010, 06:16 AM  #7 
Member Joined: Jun 2010 From: USA, Texas Posts: 85 Thanks: 0  Re: [TRIG] Indentities
Doesn't the Pythagorean Theorem state: 1 + cot²x = csc²x Not: cot²x  1 = csc²x Or is it the same thing? 
June 15th, 2010, 06:31 AM  #8 
Member Joined: Jun 2010 From: USA, Texas Posts: 85 Thanks: 0  Re: [TRIG] Indentities
And like what do these equal to: csc²x = ? cot²x = ? sec²x = ? 
June 15th, 2010, 08:09 AM  #9  
Global Moderator Joined: Dec 2006 Posts: 20,941 Thanks: 2210  Quote:
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