Results 1 to 6 of 6

Math Help - write in terms of sin and cos

  1. #1
    Newbie
    Joined
    Jul 2013
    From
    USA
    Posts
    4

    write in terms of sin and cos

    the problem asks me to write sec - tan x sin in terms of sin and cos and the answer in the book is just cos. im assuming they want me to use some identities and then find the lcd and simplify but i haven't been in school for about 6 years and my brain isn't working... please help me see how sec - tan x sin reduces to cos. thanks
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,677
    Thanks
    1618
    Awards
    1

    Re: write in terms of sin and cos

    Quote Originally Posted by sinceredoper View Post
    the problem asks me to write sec - tan x sin in terms of sin and cos and the answer in the book is just cos. im assuming they want me to use some identities and then find the lcd and simplify but i haven't been in school for about 6 years and my brain isn't working... please help me see how sec - tan x sin reduces to cos. thanks
    \sec(x)-\tan(x)\sin(x)=\frac{1}{\cos(x)}-\frac{\sin(x)}{\cos(x)}\sin(x)=\frac{1-\sin^2(x)}{\cos(x)}
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Newbie
    Joined
    Jul 2013
    From
    USA
    Posts
    4

    Re: write in terms of sin and cos

    thats what i had written out but the book is saying the answer is just cos. im reading more and i guess im supposed to use the pythagorean identity for 1 so it's cos^2 + sin^2 - sin^2 / cos, which reduces to cos^2 / cos and then just cos? if thats right please let me know. im 2 days into learning trig after a 6 year break from math. nothing is making sense. lol

    thx for quick response.
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,677
    Thanks
    1618
    Awards
    1

    Re: write in terms of sin and cos

    Quote Originally Posted by sinceredoper View Post
    thats what i had written out but the book is saying the answer is just cos. im reading more and i guess im supposed to use the pythagorean identity for 1 so it's cos^2 + sin^2 - sin^2 / cos, which reduces to cos^2 / cos and then just cos? if thats right please let me know. im 2 days into learning trig after a 6 year break from math. nothing is making sense.
    1-\sin^2(x)=\cos^2(x) and is it true that \frac{C^2}{C}=C~?
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Newbie
    Joined
    Jul 2013
    From
    USA
    Posts
    4

    Re: write in terms of sin and cos

    i get it now, i went full retard. thanks
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Prove It's Avatar
    Joined
    Aug 2008
    Posts
    11,570
    Thanks
    1428

    Re: write in terms of sin and cos

    Also note, sin, cos, tan, sec, csc and cot are all MEANINGLESS without a variable attached to them!
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Write in lowest terms
    Posted in the Algebra Forum
    Replies: 3
    Last Post: March 4th 2011, 11:56 AM
  2. Write the inverse of A in terms of the matrix A
    Posted in the Advanced Algebra Forum
    Replies: 2
    Last Post: April 15th 2010, 06:00 AM
  3. Write the expressions in terms of cosine?
    Posted in the Trigonometry Forum
    Replies: 3
    Last Post: March 11th 2009, 11:27 AM
  4. write in terms of sin and cos
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: November 2nd 2008, 12:32 PM
  5. Write Log In Terms of a and b
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: August 4th 2008, 05:20 AM

Search Tags


/mathhelpforum @mathhelpforum