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#1 2006-01-25 15:16:01

Old_dad
Member
Registered: 2006-01-25
Posts: 2

Son asked for help with trig identities.. can't seem to remember how

Can seem to remember how to prove the following identity

    tanx                sinx
-----------  =   ---------------
1 + tanx         sin x + cosx


I can get

sinx
---------
cosx
---------------
cosx + sinx
-------------
   cosx

but cannot get any further.

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#2 2006-01-25 17:15:21

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

Re: Son asked for help with trig identities.. can't seem to remember how


"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 2006-01-25 19:22:09

MathsIsFun
Administrator
Registered: 2005-01-21
Posts: 7,551

Re: Son asked for help with trig identities.. can't seem to remember how

Dad was soooo close!


"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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#4 2006-01-25 20:24:04

mikau
Member
Registered: 2005-08-22
Posts: 1,504

Re: Son asked for help with trig identities.. can't seem to remember how

Yeah, just had to multiply above and below by cos x and we would have had it.

Wish I could ask my dad for help. He went as far as calculus 2 in college but never really had to use it, so he forgot most of it. What a pity...


A logarithm is just a misspelled algorithm.

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#5 2006-01-26 01:04:32

Old_dad
Member
Registered: 2006-01-25
Posts: 2

Re: Son asked for help with trig identities.. can't seem to remember how

Thanks to all.

I keep asking him if he needs any help ... did not actually think he would take me up on it....
It really makes me feel old.

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#6 2006-01-26 04:34:12

RickyOswaldIOW
Member
Registered: 2005-11-18
Posts: 212

Re: Son asked for help with trig identities.. can't seem to remember how

My dad teaches maths in a secondary school (in the UK) yet he knows nothing about mathematics!!! yikes
A lot of state school teachers in the UK are basically baby sitters.


Aloha Nui means Goodbye.

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#7 2006-01-26 04:35:39

RickyOswaldIOW
Member
Registered: 2005-11-18
Posts: 212

Re: Son asked for help with trig identities.. can't seem to remember how

Where did you learn maths Old_dad?


Aloha Nui means Goodbye.

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#8 2006-01-26 09:26:37

MathsIsFun
Administrator
Registered: 2005-01-21
Posts: 7,551

Re: Son asked for help with trig identities.. can't seem to remember how

rickyoswaldiow wrote:

My dad teaches maths in a secondary school (in the UK) yet he knows nothing about mathematics!!!

I think it sometimes goes like this:

"Mary, our very talented mathematics teacher, has retired ... who can take over her classes?"
"Ummm ... Sam has the lightest workload"
"Congratulations Sam, you now teach Mathematics"


"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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