Results 1 to 10 of 10

Math Help - [SOLVED] More verifying that each trigonometric equation is an identity... again.

  1. #1
    Junior Member
    Joined
    Nov 2009
    Posts
    42

    [SOLVED] More verifying that each trigonometric equation is an identity... again.

    i still struggle with these;. i've been working on this one for a half hour.

    (cot^2 x -1)/(cot^2 x +1)= 2sin^2 x
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by somanyquestions View Post
    i still struggle with these;. i've been working on this one for a half hour.

    (cot^2 x -1)/(cot^2 x +1)= 2sin^2 x
    It's not an identity. The RHS should be 1 - 2 sin^2 x.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member
    Joined
    Nov 2009
    Posts
    42
    sorry about that. i worked on the corrected problem for a half hour.
    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 somanyquestions View Post
    sorry about that. i worked on the corrected problem for a half hour.
    Substitute \cot x = \frac{\cos x}{\sin x} into the LHS. Then multiply the resulting numerator and denominator by \sin^2 x. Then apply a well known double angle formula.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member
    Joined
    Nov 2009
    Posts
    42
    i never learned those formulas.. or maybe we're not there yet?? i don't know.

    so..
    (cot^2 x -1)/(cot^2 x +1)= 1-2sin^2 x

    [(cos^2 x/ sin^2 x) -1] / [(cos^2 x/sin^2 x) +1]

    [(cos^2x*sin^2 x/sin^4 x) -1]/[(cos^2x*sin^2 x/sin^4 x) +1]


    ?
    then.. i don't know. i'll just ask my teacher, maybe she has some way to do it using methods i have already learned.
    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 somanyquestions View Post
    i never learned those formulas.. or maybe we're not there yet?? i don't know.

    so..
    (cot^2 x -1)/(cot^2 x +1)= 1-2sin^2 x

    [(cos^2 x/ sin^2 x) -1] / [(cos^2 x/sin^2 x) +1]

    Mr F says: When you multiply the numerator and denominator of the above line you get {\color{red}\frac{\cos^2 x - \sin^2 x}{\cos^2 x + \sin^2 x}}. I don't know how you got the line below.

    [(cos^2x*sin^2 x/sin^4 x) -1]/[(cos^2x*sin^2 x/sin^4 x) +1]


    ?
    then.. i don't know. i'll just ask my teacher, maybe she has some way to do it using methods i have already learned.
    Are you saying you never learned that cot x = 1/tan x and that you don't know that tan x = sin x/cos x? And you're unfamiliar with the fact that \cos^2 x = 1 - \sin^2 x? (you don't actually need any double angle formula).
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Junior Member
    Joined
    Nov 2009
    Posts
    42
    Quote Originally Posted by mr fantastic View Post
    Are you saying you never learned that cot x = 1/tan x and that you don't know that tan x = sin x/cos x? And you're unfamiliar with the fact that \cos^2 x = 1 - \sin^2 x? (you don't actually need any double angle formula).
    i am. i won't ask for help on these type of questions anymore. you make me feel unintelligent. this is why i need help. i can't even multiply this right.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by somanyquestions View Post
    i am. i won't ask for help on these type of questions anymore. you make me feel unintelligent. this is why i need help. i can't even multiply this right.
    If you're given questions like the one you posted then you're expected to know the things I mentioned in my previous post. The application of these things in a particular question is what you can be helped with. But if you don't know these things, then you need to go back to your class notes and textbook and review that material so that you do know them.
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Junior Member
    Joined
    Nov 2009
    Posts
    42
    Quote Originally Posted by mr fantastic View Post
    If you're given questions like the one you posted then you're expected to know the things I mentioned in my previous post. The application of these things in a particular question is what you can be helped with. But if you don't know these things, then you need to go back to your class notes and textbook and review that material so that you do know them.
    i know them except the angle rule or some other that people have been saying to me.. i don't know why i haven't learned that in class yet. i guess i just can't multiply them properly half the time. i'll work on it.
    Follow Math Help Forum on Facebook and Google+

  10. #10
    Junior Member
    Joined
    Nov 2009
    Posts
    42
    Quote Originally Posted by mr fantastic View Post
    Are you saying you never learned that cot x = 1/tan x and that you don't know that tan x = sin x/cos x? And you're unfamiliar with the fact that \cos^2 x = 1 - \sin^2 x? (you don't actually need any double angle formula).
    i misread something you said. sorry. no more posts on this one.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 4
    Last Post: March 21st 2010, 09:29 PM
  2. Replies: 6
    Last Post: March 21st 2010, 08:17 PM
  3. verifying a trigonometric identity
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: May 3rd 2009, 11:56 AM
  4. Verifying Trigonometric Identity
    Posted in the Pre-Calculus Forum
    Replies: 4
    Last Post: May 16th 2008, 09:57 AM
  5. Verifying that the equation is an identity
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: April 8th 2008, 02:31 AM

Search Tags


/mathhelpforum @mathhelpforum