SOLUTION: Hi. I'm not sure how to find the answer of this kind of equation: 2cos(3x)+1=0. now, i can get as far as cos(3x)= -.5 and replace the 3x with an "a" and divide. I now get 3x=2pi/3

Question 64455: Hi. I'm not sure how to find the answer of this kind of equation:
2cos(3x)+1=0. now, i can get as far as cos(3x)= -.5 and replace the 3x with an "a" and divide. I now get 3x=2pi/3 and 4pi/3. my problem is that i have to solve over a (0, 2pi] domain, and i'm not sure how to alter the domain once i divide my answers by 3. please help! thanks.
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
2cos(3x)+1=0
cos(3x)=-1/2
Take the arccos of both sides to get:
3x=120 degrees or (2/3)pi radians
x=40 degrees or (2/9)pi radians
Cheers,
Stan H.
RELATED QUESTIONS
2sin^2x+7cosx-5=0 This is as far as I've gotten, not sure how to finalize the answer... (answered by lwsshak3)

Write cos^4(3x) in terms of cosines all to the 1st power. FIND LCD & SIMPLIFY! I GOT... (answered by Alan3354)

Hi, I am not sure how to approach this question, any help is appreciated. Thanks!... (answered by stanbon)

find all solutions of the equation {{{ 4x-8 sqrt( x )-5=0 }}}. please show me every... (answered by ewatrrr)

Hi there! I have never solved a problem like this before so I am not sure how to start.... (answered by Alan3354)

Please help me solve the following question. I have tried to find examples of how to... (answered by Nate)

Hi, I'm confused about solving for this trig equation: 3cos(x)+cos^2(x)+2=sin^2(x). I (answered by ikleyn)

2cos(5 theta) + square root of 3 = 0 I have tried making theta equal 5theta and... (answered by lwsshak3)

hi I have a question and I am unable to answer it so here goes: Show that the area (answered by josgarithmetic)