text: evalutate cos(tan^-1(x/2) or cos(arctan (x/2)....same thing?   first, they are the same next, when it comes to evaluating them, we know that the part in the parenthesis means that tan(theta)=x/2 since tan is y/x, then y = x and x = 2 to find r, use the pythagorean theorem so that x^2 + 2^2 = r^2 making r = the square root of (x^2 + 4) so, the cos, being x/r would be 2/square root of(x^2 + 4) if you wanted to remove the radical from the denominator, multiply both sides by the square root of (x^2 + 4) and simplify to get the final answer of (2*the square root of (x^2 + 4))/(x^2 + 4)