Results 1 to 10 of 10

Math Help - 2sin^2(x)-sin(x)=3

  1. #1
    Newbie
    Joined
    Feb 2008
    Posts
    3

    2sin^2(x)-sin(x)=3

    2sin^2(x)-sin(x)=3 find for all values of x. this is pre-calc stuff.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,663
    Thanks
    298
    Awards
    1
    Quote Originally Posted by pd1dish View Post
    2sin^2(x)-sin(x)=3 find for all values of x. this is pre-calc stuff.
    This is a quadratic equation problem.

    Let y = sin(x). Then your equation becomes:
    2y^2 - y = 3

    Solve this for y and then take the inverse sine of the two answers.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Feb 2008
    Posts
    3
    what would i do from there...i have no clue what is going on in my pre-calc class right now so if some1 can just post every step, that would be really helpful and i have a couple more problems similar to this one and me seeing each step will help me with those.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by pd1dish View Post
    what would i do from there...i have no clue what is going on in my pre-calc class right now so if some1 can just post every step, that would be really helpful and i have a couple more problems similar to this one and me seeing each step will help me with those.
    Do you know how to solve a quadratic equation?
    Do you know that -1 \leq \sin x \leq 1 and so there are no real solutions to something like \sin x = \frac{3}{2} \,?
    Do you know how to solve \sin x = -1\, ?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Feb 2008
    Posts
    3
    w/e...u guys arent helping. all i wanted was a step by step process. im going to a different site that actually gives u the answer instead of making me figure it out.
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by pd1dish View Post
    w/e...u guys arent helping. all i wanted was a step by step process. im going to a different site that actually gives u the answer instead of making me figure it out.
    You've been given quite a bit of help, actually. I'm sorry that the effort required of you to take that help on board is too great.

    Simple yes or no answers to my questions would have been useful in pinpointing your exact troubles.

    Your mathematical difficulties seem to extend beyond trigonometry - you're encouraged to get as much extra help as possible from your instructor.

    And the answer is x = \frac{(4n+3) \pi}{2} where n is an integer.
    Last edited by mr fantastic; February 20th 2008 at 03:22 AM. Reason: Fixed a mistake in the answer - obviously my answer to the third question was >no< lol!
    Follow Math Help Forum on Facebook and Google+

  7. #7
    is up to his old tricks again! Jhevon's Avatar
    Joined
    Feb 2007
    From
    New York, USA
    Posts
    11,663
    Thanks
    3
    Quote Originally Posted by pd1dish View Post
    w/e...u guys arent helping. all i wanted was a step by step process. im going to a different site that actually gives u the answer instead of making me figure it out.
    they are helping more than you know. helping you figure out things for yourself is better. when you're in an exam, who is the one who's going to have to figure stuff out? you might as well get used to it from now
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Math Engineering Student
    Krizalid's Avatar
    Joined
    Mar 2007
    From
    Santiago, Chile
    Posts
    3,654
    Thanks
    11
    Quote Originally Posted by pd1dish View Post
    w/e...u guys arent helping.
    They actually did.

    Quote Originally Posted by pd1dish View Post
    all i wanted was a step by step process.
    This depends, you just posted the question and you didn't even show a progress. Do you want a coke, cigarette, something else while someone is giving you a full solution?

    Quote Originally Posted by pd1dish View Post
    im going to a different site that actually gives u the answer instead of making me figure it out.
    It's not a duty to give you a full solution, from a beginning you didn't specify anything.

    Of course, the door is big enough. (Do you think that you scare us with such comment, rating's site will decay?)
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Junior Member
    Joined
    Feb 2008
    From
    Melbourne
    Posts
    27
    Quote Originally Posted by mr fantastic View Post
    You've been given quite a bit of help, actually. I'm sorry that the effort required of you to take that help on board is too great.

    Simple yes or no answers to my questions would have been useful in pinpointing your exact troubles.

    Your mathematical difficulties seem to extend beyond trigonometry - you're encouraged to get as much extra help as possible from your instructor.

    And the answer is x = \frac{(2n+1) \pi}{2} where n is an integer.
    Upon doing the maths

    2 sin^2(x) - sin(x) = 3

    2 sin ^2(x) - sin(x) - 3 = 0

    let sin(x)=y

    2y^2 - y - 3 = 0

    (2y-3)(y+1) = 0

    therefore

    sin x = 3/2 and -1

    since -1 <= sin <= 1

    sin x = -1

    x = sin^-1 (-1)

    x = 3pi / 2 + 2pi(n) where n is an element of Z

    sorry if im wrong =[ but like that seems right XD



    I think your answer is solved for = 1 not = 3

    edit .. or you used 1 instead of -1 ... ?

    sorry if im wrong >.>
    Last edited by Charbel; February 20th 2008 at 02:59 AM.
    Follow Math Help Forum on Facebook and Google+

  10. #10
    femmekarammel
    Guest
    I'm not even taking trig and this is an easy problem. People: learn to do some work instead of having other people do it for you.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [2sin^2(x/2) ] / [2sin(x/2)cos(x/2)]
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: December 13th 2011, 06:15 AM
  2. How to solve -2sin(t)+ cos(t) =0
    Posted in the Trigonometry Forum
    Replies: 6
    Last Post: October 23rd 2010, 10:53 AM
  3. solve 2sin(x-45)=1
    Posted in the Trigonometry Forum
    Replies: 2
    Last Post: October 6th 2010, 01:48 AM
  4. prove that a^2sin(A-C)=
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: December 10th 2009, 11:18 PM
  5. int x^2sin^-1(x)
    Posted in the Calculus Forum
    Replies: 4
    Last Post: August 6th 2007, 09:00 PM

Search Tags


/mathhelpforum @mathhelpforum