The inverse tan of 1, ie tan-1 (1) is a very special value for the inverse tangent function. Remember that tan-1(x) will give you the angle whose tan is x . Therefore, tan-1 (1) = the angle whose tangent is 1. It's also helpful to think of tangent
The Value of the Inverse Tan of 1
As you can see below, the inverse tan-1 (1) is 45° or, in radian measure, Π/4. It is helpful to think of tangent as the ratio of sine over cosine, ie: 
. Therefore, tan(Θ) to equal 1, sin(Θ) and cos(Θ) must have the same value.
The answer is at 
and, of course, sine these trig functions are cyclical you can generalize 
