Results 1 to 14 of 14

Math Help - Help with the Trigonometry Equation please!

  1. #1
    Newbie
    Joined
    Sep 2012
    From
    UK
    Posts
    20

    Help with the Trigonometry Equation please!

    Hi guys,
    I am stressing myself out coz i dont know how to do this question.

    Question being:
    2cos(x-30)=1
    0o≤X≤360o

    I think you start by dividing both sides by 2 to get: cos(x-30)=1/2, but dont know what you do from here!

    Thanks in advance
    Dan

    ps. could you please explain the working so I can understand it a bit better?

    Thanks
    Last edited by Danthemaths; February 21st 2013 at 08:11 AM.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with the Trigonometry Equation please!

    Look at the graph of cos(x) (note that it's not cos(x - 30)). For which values of x is it the case that cos(x) = 1/2? For each y is such that cos(y) = 1/2, we need to find x such that x - 30 = y. Find all such x's and then select those that are between 0 and 360.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Senior Member
    Joined
    Feb 2013
    From
    Saudi Arabia
    Posts
    441
    Thanks
    86

    Re: Help with the Trigonometry Equation please!

    Danthemaths

    divide first by 2 to obtain cos(x-30)=1/2
    which angle has cos =1/2 of course 60 therefore cos(X-30)=cos60
    and of course the answer is x-30=60 which gives you x=90...study more the trigonometric equations...Tere are some other solutions negative but since you are restricted to 0....360 you cannot consider them.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with the Trigonometry Equation please!

    Quote Originally Posted by MINOANMAN View Post
    the answer is x-30=60 which gives you x=90... Tere are some other solutions negative but since you are restricted to 0....360 you cannot consider them.
    There is another solution between 0 and 360.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Sep 2012
    From
    UK
    Posts
    20

    Re: Help with the Trigonometry Equation please!

    There is another solution between 0 and 360.
    Thank you Minoanman!
    and ema, is the other solution 360-90? which will give 570?

    So the answers will be
    x=90
    x=360-90=570

    Is this correct?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with the Trigonometry Equation please!

    Quote Originally Posted by Danthemaths View Post
    is the other solution 360-90? which will give 570?

    So the answers will be
    x=90
    x=360-90=570
    No, I suggest you follow the algorithm in post #2. And how do you get 570 from 360 - 90?
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Newbie
    Joined
    Sep 2012
    From
    UK
    Posts
    20

    Re: Help with the Trigonometry Equation please!

    haha lol typo!

    I meant 270 :P
    Follow Math Help Forum on Facebook and Google+

  8. #8
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with the Trigonometry Equation please!

    Quote Originally Posted by Danthemaths View Post
    I meant 270 :P
    This is still not a solution of the original equation. You can check that 2cos(270 - 30) ≠ 1.
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Newbie
    Joined
    Sep 2012
    From
    UK
    Posts
    20

    Re: Help with the Trigonometry Equation please!

    i still dont understand how u get second answer...?
    Follow Math Help Forum on Facebook and Google+

  10. #10
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with the Trigonometry Equation please!

    Quote Originally Posted by Danthemaths View Post
    i still dont understand how u get second answer...?
    And I still don't understand what prevents you from following the steps in post #2. What exactly don't you understand about them?
    Follow Math Help Forum on Facebook and Google+

  11. #11
    Newbie
    Joined
    Sep 2012
    From
    UK
    Posts
    20

    Re: Help with the Trigonometry Equation please!

    ahh think this is right.

    x=330?

    If so, thanks alot guys
    Follow Math Help Forum on Facebook and Google+

  12. #12
    MHF Contributor
    Joined
    Oct 2009
    Posts
    5,537
    Thanks
    778

    Re: Help with the Trigonometry Equation please!

    Quote Originally Posted by Danthemaths View Post
    x=330?
    Yes. We have cos(300) = cos(360 - 60) = cos(-60) = cos(60) = 1/2, so x - 30 = 300 implies that x = 330 is a solution.
    Follow Math Help Forum on Facebook and Google+

  13. #13
    Newbie
    Joined
    Sep 2012
    From
    UK
    Posts
    20

    Re: Help with the Trigonometry Equation please!

    thanks for helping me xD
    Follow Math Help Forum on Facebook and Google+

  14. #14
    Newbie
    Joined
    Sep 2012
    From
    UK
    Posts
    20

    Re: Help with the Trigonometry Equation please!

    Look at the graph of cos(x) (note that it's not cos(x - 30)). For which values of x is it the case that cos(x) = 1/2? For each y is such that cos(y) = 1/2, we need to find x such that x - 30 = y. Find all such x's and then select those that are between 0 and 360.
    Also, on this website you used for the graph, it a pretty neat site. How did you get the x axis to appear as degrees instead of the default {0,1,2,3,4..}?
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Trigonometry equation 2
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: December 8th 2009, 11:06 PM
  2. trigonometry equation
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: June 2nd 2009, 08:06 AM
  3. trigonometry equation
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 3rd 2008, 03:29 PM
  4. trigonometry equation
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: May 1st 2007, 05:20 AM
  5. trigonometry equation
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: April 15th 2007, 11:02 AM

Search Tags


/mathhelpforum @mathhelpforum