Given sin = in quadrant III, tan = in quadrant II; find the value of sin( + ):

I've posted my solution -- which the answer key says is wrong -- here, http://imagebin.ca/img/tnINM0J.png .

Please tell me what I'm doing wrong.

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- Mar 17th 2010, 07:40 PMbeardedoneder[SOLVED] Cosine of the Sum of Two Angles
Given sin = in quadrant III, tan = in quadrant II; find the value of sin( + ):

I've posted my solution -- which the answer key says is wrong -- here, http://imagebin.ca/img/tnINM0J.png .

Please tell me what I'm doing wrong. - Mar 17th 2010, 07:58 PMbigwave
- Mar 17th 2010, 08:01 PMskeeter
- Mar 17th 2010, 08:08 PMpickslides
- Mar 17th 2010, 08:22 PMSoroban
Hello, beardedoneder!

Sorry, I couldn't read your work.

Quote:

Given: .

find the value of: .

We have: .

is in a right triangle with:

Pythagorus says: .

. . In Quadrant III:

Hence: . .[1]

We have: .

is in Quadrant II with:

Pythagorus says: .

Hence: . .[2]

We want: .

Substitute [1] and [2]:

- Apr 7th 2010, 05:02 PMbeardedonederAnswer Key Was Wrong
- Apr 7th 2010, 05:11 PMbeardedonederDid you mean to say, ...
- Apr 7th 2010, 05:14 PMbeardedonederDid you mean to say, ...