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Math Help - Co-functions help needed..

  1. #1
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    Co-functions help needed..

    Hey guys,
    Due to the lecturer not knowing himself, I don't know how exactly to approach some of the following problems.

    Simplify:
    1. sec(90+x)sin(180+x) + sin(-x)

    2. __sin(-x)_ ______1______ __tanx___
    sin(180+x) + secx.sin(90+x) - cot(90+x)

    Solve for x:
    1. 3cot(90+x) = tanx.sinx

    2. tan(90-x) = sec(3x+10)cotx

    I feel a bit stupid asking, BUT then, the only stupid question is the one not asked!

    Thanks in advance for any help and/or advice..
    Riaan.
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  2. #2
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    Re: Co-functions help needed..

    Quote Originally Posted by riaanj View Post
    Simplify:
    1. sec(90+x)sin(180+x) + sin(-x)
    The first thing I usually do is to get everything in terms of sine and cosine. sec(x) = 1/cos(x), and we have the sum of angles formula:
    cos(a + b) = cos(a) ~ cos(b) - sin(a) ~ sin(b)

    So what is cos( 90 + x)?

    The same goes for sine:
    sin(a + b) = sin(a) ~ cos(b) + sin(b) ~ cos(a)

    See what you can do with this. If you need more help with it, simply ask.

    -Dan
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  3. #3
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    Re: Co-functions help needed..

    Ok, so I had class tonight and I'm gonna try this one quick..
    sec(90+x)sin(180+x) + sin(-x)
    = -cscx(-sinx)+(-sinx)
    = -1/sinx(-sinx)-sinx
    = 1-sinx

    I'll try the rest after I had some sleep..
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