atan

Computes the arc tangent of the value x; the returned value is an angle in the range from -PI/2 to PI/2 radians.

expect fun atan(x: Double): Double(source)

import kotlin.math.atan
import kotlin.math.PI

fun main() {
    val value = 1.0
    val angleInRadians = atan(value)
    val angleInDegrees = angleInRadians * 180 / PI

    println("atan($value) = $angleInRadians radians")
    println("atan($value) = $angleInDegrees degrees")
}

Source