To write the composed trigonometric function sin(arctan x) in terms of x, we first need to use the definition of the inverse trigonometric function arctan(x).
arctan(x) is defined as the angle whose tangent is x. So, let's consider a right triangle with opposite side = x and adjacent side = 1. Then, the tangent of the angle θ in this triangle is x/1 = x. Using the Pythagorean theorem, the hypotenuse of the triangle is sqrt(1 + x^2).
Now, we can find sin(arctan(x)) using the definition of sine in a right triangle as opposite side / hypotenuse. So, sin(arctan(x)) = x / sqrt(1 + x^2).
Therefore, sin(arctan(x)) = x / sqrt(1 + x^2).
This is the composed trigonometric function sin(arctan x) in terms of x.