sadistic calculus professor

This is a discussion on sadistic calculus professor within the A Brief History of Cprogramming.com forums, part of the Community Boards category; We're doing volumes of rotated functions. I've got most of them done, but I just have to solve for x ...

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    sadistic calculus professor

    We're doing volumes of rotated functions. I've got most of them done, but I just have to solve for x in this equation, and NO identities are coming to mind... and I can't find any that apply in my lists or on the internet. Can anybody see a way to solve for x here? (Algebraically, not graphically...)

    Code:
    9     cos(x)
    --  = -------
    16    sin(2x)

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    and the Hat of Guessing tabstop's Avatar
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    NO identities are coming to mind? You can't find an identity for sin(2x)?

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    Wow I'm stupid... It's been 3 years since my last math class.

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    dude I hear you. I took prob and stat last semester after roughly 2 or three years of not taking any math courses and felt like an idiot because I couldn't do integrals or basic stuff. I remembered quickly with the power of google and the like.
    Here to Deceive, Inveigle, Obfuscate Since 1945

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    Registered User Kernel Sanders's Avatar
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    sin(2x) = 2*sin(x)*cos(x)

    9/16 = cos(x) / (2 * sin(x) * cos(x))
    9/8 = 1/sin(x)
    sin(x) = 8/9
    x = arcsin(8/9)

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    Quote Originally Posted by sean View Post
    Wow I'm stupid... It's been 3 years since my last math class.
    Don't worry about it man, once you get back into the swing of things *pushes up glasses...pockets calculator* this math stuff will be nothing but a reflex for ya.
    I'm not immature, I'm refined in the opposite direction.

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    The superhaterodyne twomers's Avatar
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    It's worse when they give you something like:

    x + sin( x ) = 0.3

    or something. Can't solve it analytically and it drives me mad!

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    Mad OnionKnight's Avatar
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    When you have to integrate sin(x)^8 dx is when I go SCREW YOU

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    Malum in se abachler's Avatar
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    Quote Originally Posted by sean View Post
    We're doing volumes of rotated functions. I've got most of them done, but I just have to solve for x in this equation, and NO identities are coming to mind... and I can't find any that apply in my lists or on the internet. Can anybody see a way to solve for x here? (Algebraically, not graphically...)

    Code:
    9     cos(x)
    --  = -------
    16    sin(2x)
    -X / 2 dX

    they should have covered the relation between sine and coine as derivatives of each other.
    Until you can build a working general purpose reprogrammable computer out of basic components from radio shack, you are not fit to call yourself a programmer in my presence. This is cwhizard, signing off.

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    Yes, sine and cosine have a relationship as derivatives, but when one is a function of x and the other is a function of 2x, it's a more complex relationship. The way to simplify it was to use sin(2x) = 2sin(x)cos(x), and therefore the whole expression simplifies to 1/2sin(x).

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