def _calc_c(H, r_eq):
    """
    Calculates the b coefficient used to calculate the distance from the satellite
    to a point P

    Parameters
    ----------
    H : int
        GOES-16 projection perspective point height, in meters
    r_eq : int
        GOES-16 semi-major axis of projection, in meters

    Returns
    -------
    float
    """
    return (H**2 - r_eq**2)