Why the trigonometry results are different

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

Answer 1

[Peter Perkins]

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.

Answer 2

[David Sanchez]

The different result between tan(90) and tan(pi/2) is obvious.

1.6331e+16 might be considered equal to inf

Answer 3

[Iain]

That's likely just the effect of small numerical errors.

After all, according to matlab,

 1E300 + 1 - 1E300 = 0, and 
 1E300 - 1E300 + 1 = 1

Answer 4

[Adam]

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