import math


def t_o(tdb, tr, v):
    """Calculates operative temperature in accordance with ISO 7726:1998 [5]_

    Parameters
    ----------
    tdb: float
        air temperature, [°C]
    tr: float
        mean radiant temperature temperature, [°C]
    v: float
        air speed, [m/s]

    Returns
    -------
    to: float
        operative temperature, [°C]
    """

    return (tdb * math.sqrt(10 * v) + tr) / (1 + math.sqrt(10 * v))