# quick sine question

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(i know this is stupid, i'm a mor0n at math) is inverse sin theta equals to: 1/sin(theta) ? thanks.

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No, you need to use asin(theta) (if C/C++ is your flavour). In textbooks this is often presented as sin-1(theta), but it's not to be confused with sin(theta)-1 :)

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ok thanks.

theta = arcsin(y/r) right?

then is theta = sin(y/r)?

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theta = arcsin(y/r)
sin(theta) = sin(arcsin(y/r))
sin(theta) = y/r

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Quote:
 Original post by lonesocktheta = arcsin(y/r)sin(theta) = sin(arcsin(y/r))sin(theta) = y/r

if theta = arcsin(y/r), is theta = sin(r/y)?

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No.

If theta = arcsin(y/r), then y/r = sin(theta)

You seem to be used to thinking of inverses as swapping numerators with denominators. That's the case only for inverting multiplications, but functions are a different story. Inverting doesn't necessarily have anything to do with turning numbers "upside-down". The inverse of an operation is simply something that "undoes" that operation.

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if you image sin and arcsin, cos and arccos, tan and arctan to all be C functions, then Sin(float angle), gives you the ratio of the opposite side to the hypotenuse (a ratio), whereas Arcsin(float ratio), works backwards giving you the angle from the ratio. How can they possibly be the same, when an angle is dependent on the measuring system used (i.e 360 deg or 2pi)?

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Quote:
 Original post by _nomad_if theta = arcsin(y/r), is theta = sin(r/y)?

no, even exchanging (y/r) for (r/y) does not work.

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ah...ok...thank you guys! :) obviously, i'm no good at math...:)...i'll keep trying to learn though. thanks!

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