cos returns wrong values?

Question

I have a strange problem with the standard cos function of cmath/math.h. Apparently under some circumstances it returns a wrong or simply undefined value.

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Answer 1

cos expects radians, you are giving it degrees. Multiply your input value by 3.14159/180, and you will get the right answer.

Answer 2

cos(PI/2) = 0, not 1.

Answer 3

I don't know if you're passing radian or degrees... But your value of foo is near PI/2. So you get cos(foo) = 0 and sin(foo) = 1 (what you expected?)