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**Identity****Member**- Registered: 2007-04-18
- Posts: 934

Find the exact value of

Is there a way to do this without drawing a triangle, what's the most efficient way? The book doesn't say which way it should be done.

Also, when finding

using triangles, you could have opp/adj = 2/-1 or opp/adj = -2/1 ... so couldn't there be 2 possible solutions?

*Last edited by Identity (2008-12-24 21:29:59)*

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**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

Trying both roots, the positive is correct, the negative incorrect

...

infact, it turns out that you must take the negative root, if x is negative, and the positive root if x is positive

*Last edited by luca-deltodesco (2008-12-24 22:28:06)*

The Beginning Of All Things To End.

The End Of All Things To Come.

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**Identity****Member**- Registered: 2007-04-18
- Posts: 934

Wow, very nice ! Thanks luca

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**Daniel123****Member**- Registered: 2007-05-23
- Posts: 663

I think it's much quicker/easier/nicer to draw a triangle. The identities luca's used all come from triangles anyway.

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**Monox D. I-Fly****Member**- Registered: 2015-12-02
- Posts: 860

Daniel123 wrote:

I think it's much quicker/easier/nicer to draw a triangle. The identities luca's used all come from triangles anyway.

Agree. By looking at the sine value, we know that the height is 4 and the hypotenuse is 5. Thus, with the Pythagorean theorem we know that the base is 3.

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