double acos(
num x
)

Converts x to a double and returns the arc cosine of the value.

Returns a value in the range -PI..PI, or NaN if x is outside the range -1..1.

Source

/**
 * Converts [x] to a double and returns the arc cosine of the value.
 *
 * Returns a value in the range -PI..PI, or NaN if [x] is outside
 * the range -1..1.
 */
external double acos(num x);