import math


def arc_chord_length(radius: float, sagitta: float) -> float:
    """Returns the chord length for an arc defined by `radius` and
    the `sagitta`_.

    Args:
        radius: arc radius
        sagitta: distance from the center of the arc to the center of its base

    """
    return 2.0 * math.sqrt(2.0 * radius * sagitta - sagitta * sagitta)