def GetTringleArea(a, b, c):
    """Get a tringle area.
    Args:
        a: an edge length.
        b: an edge length.
        c: an edge length.
    Returns:
        the area of the tringle.
    """
    s = (a + b + c) / 2.0
    return (s*(s-a)*(s-b)*(s-c)) ** 0.5