Why the trigonometry results are different

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Madhu
Madhu 2014-8-21
回答： Peter Perkins 2014-8-22
Why there is a difference in the results. in degrees it is showing inf and in radians a different result?
>> a=tan(90)
a =
-1.9952
>> b=tand(90)
b =
Inf
>> c=tan(pi/2)
c =
1.6331e+16

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采纳的回答

Peter Perkins
Peter Perkins 2014-8-22
1.6331e+16 is the right answer. Remember that pi/ is irrational. There is no way to represent it in double precision. The tangent of the double precision value pi/2 evaluates to is 1.6331e+16. That's the main reason for the existence of tand -- 90 is exact.

更多回答（3 个）

David Sanchez
David Sanchez 2014-8-21
The different result between tan(90) and tan(pi/2) is obvious.
1.6331e+16 might be considered equal to inf
Iain
Iain 2014-8-21
That's likely just the effect of small numerical errors.
After all, according to matlab,
1E300 + 1 - 1E300 = 0, and
1E300 - 1E300 + 1 = 1
Adam
Adam 2014-8-21
tan is asymptotic at 90 degrees, but pi/2 will not evaluate to the precise equivalent with a numerical estimate of pi so its result will not be precisely on the asymptote

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