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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_apex(self, lat, height=None):
 """ Calculate apex height Parameters lat : (float) Latitude in degrees height : (float or NoneType) Height above the surface of the earth in km or NoneType to use reference height (default=None) Returns apex_height : (float) Height of the field line apex in km """

        lat = helpers.checklat(lat, name='alat')
        if height is None:
            height = self.refh

        cos_lat_squared = np.cos(np.radians(lat))**2
        apex_height = (self.RE + height) / cos_lat_squared - self.RE

        return apex_height