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# Simple math question about Sin, Cos, Tan

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Hi, That''s a pretty easy question. I have a triangle, i got the two lenght of the sides, but not the hypotenuse. I try to find the angle. Like this: The formula : tan (ang) = long1 / long2 The answer : ang = tan-1 (long1 / long2) It''s tan at power -1... So i can i code this Line in c/c++ ?! c dont have any tan-1 fnc. Thanks for your help ?! LowRad

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What you''re looking for for is arctan(), that''s the inverse cosine function, as is arcsin, etc.

ByteMe95::~ByteMe95()

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I too had the same problem. But it''s easy to solve
use 1/tan(Same with Sin, Cos). It''s the same as tan-1

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I beg to differ:

cos(90 degrees) = 0
cos-1(0) = 90 degrees
1/cos(90 degrees) = divide by zero error

plus it''s not right non-general rule anyway. Where did you study maths? And don''t claim it works in radians because it doesn''t.

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Mindwipe, that''s completely wrong, where did you come up with that???

Just use arccos()

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I think mindwipe read "tan()-1" as "tan() to the -1 power" which is 1/tan() of course

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arctan(x) isn't the same as 1/tan(x). arctan(x) means: "the inverse function of tan", it's not the "inverse result of tan(x)".
To find the angle use:

theta = arctan(length_y/length_x);

Do not invert the sides. length_y is the opposite side, and length_x is the adjacent side.

Edited by - blazter on July 21, 2000 5:43:38 PM

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Anonymous Poster> Yup that was what I ment. I''ve actally used it. And it works. Well, I no master on math. Due to lack of knowledge.

Just wanted to try to help

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Umm, are we assuming this is a right triangle? Those trig identities only work for a right triangle, don''t they? I''ve almost got an AA in Math on accident ...

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I don't know what is a right triangle in English. Do you mean that one of the angles must be 90 degrees ?
If so, yes it's right. These trig. functions only work on orthogonal coord. and on right triangles. By the way only a triangle with a angle of 90 degrees can have a hypotenuse.

Edited by - blazter on July 24, 2000 1:20:30 PM

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