Math Is Fun Forum

jaycm610

Member

Registered: 2009-10-22

Posts: 1

Trignonmetry: proving identities

Hey guys! I'm new on this forum. I'm 17, and I need some help with Trig if i'm gonna graduate.

Here's this problem. I need to prove this identity. I worked on this problem for an hour, and have no clue what to do.
   
cosx- (cosx/1-tanx) = sinxcosx/sinx-cosx

Thanks in advance.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Trignonmetry: proving identities

Hi jaycm610;

2 things first:

1) Use parentheses to remove ambiguities:

cosx- (cosx/1-tanx) = sinxcosx/sinx-cosx would have been much easier to understand if you would have written it like this:

cosx - cosx / (1 - tanx) = (sinx cosx) / (sinx - cosx) is clear. Also use spaces for readability. I remember a teacher complaining once that my work was unreadable so she just marked me wrong. She was right!

2) Provide the work you did so that the exact spot where you are going wrong can be found.

To solve this basically I am going to choose 1 side,( usually the more complicated one) and try to make it look like the other side. Here I start with the the left.

Clean up the left hand side.

Last edited by bobbym (2009-10-22 22:10:44)

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