Homework Help: Unit circle problems (ive wikied and googled)

1. Oct 27, 2009

ndmp

1. The problem statement, all variables and given/known data
sin3x=.966 then x could be equal to (answer in degrees)

2. Relevant equations
solving trigonometric equations

3. The attempt at a solution
sin3x=3sinx
3sinx=.966
sinx=.966/3
sinx=.322
cos^2x + sin^2x=1 (pythagorean theory)
cos^2x +.322^2=1
1-.322^2=cos^2x
lol i get stuck i dont even know if im on the right track.

2. Oct 27, 2009

cristo

Staff Emeritus
Does sin(3x) equal 3*sin(x)?

3. Oct 27, 2009

ndmp

no that has not been proven, its just a track i thought i could go down. The only information that has been given was in step 1. Are u allowed to say that sin(3x) = 3 sin(x) is that a proven law?

4. Oct 27, 2009

ndmp

thanks for your help i have been trawling wikis and googling just to get a worked example... And i wont be able to sleep if i cant figure it out lol :P

It might help i know that the answer to sin3x=.966, that x =25 degrees, i just dont know how to prove it

5. Oct 27, 2009

cristo

Staff Emeritus
For starters, the question in your post doesn't sound like it is the exact question you are asked to solve. Perhaps it will help if you copy verbatim.

Still, no, it is not true that sin(3x)=3sin(x). The way I would solve your problem would be to simply take the inverse sine of each side of your equation.

6. Oct 27, 2009

ndmp

that was the question unfortunately, it had a multiple choice aspect :(. with 5 different degree answers.

So 3x = asin .966
3x=75
x=25 thanks so much :PPPPPP