Given the equation cos2x +7cosx-3 = 0 find the tan value of x

I've tried using 2cos^2x-1 +7cosx-3=0 but I don't know what to do next??

and one more: sin 105° - sin 15° = ???

Please help. Thanks

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- November 13th 2009, 05:09 AMSodaCupTrigonometry equation?
Given the equation cos2x +7cosx-3 = 0 find the tan value of x

I've tried using 2cos^2x-1 +7cosx-3=0 but I don't know what to do next??

and one more: sin 105° - sin 15° = ???

Please help. Thanks - November 13th 2009, 05:56 AMSoroban
Hello, SodaCup!

Quote:

Given the equation: . , find

I've tried using: .

but I don't know what to do next.

How about combining the -1 and -3?

Factor: .

And we have two equations to solve:

. .

. .

Therefore: .

Quote:

Evaluate: .

So that: .

Then: .

Note that: .

- November 13th 2009, 07:01 AMSodaCup
- November 13th 2009, 08:33 AMstapel
- November 13th 2009, 09:07 AMSodaCup
- November 13th 2009, 09:11 AMstapel
- November 13th 2009, 10:08 AMSodaCup