Find cos(arctan(2)).
cos (arctan (2))
Let arctan (2) = θ
This implies that
tan θ = 2 = 2 / 1 = y / x
And cos θ = x / r
And r = sqrt ( x^2 + y^2) sqrt (1^2 + 2^2) = sqrt (5)
So
cos (arctan (2)) =
cos θ = 1 /sqrt (5) = sqrt (5) / 5