protected static function root( $amount, $periods )
	{
		Deprecation::getInstance()
			->setErrorVersion( '0.8.5' )
			->setExceptionVersion( '0.9' )
			->message( sprintf(
				'Please use %s (%s) instead',
				'public library "CeusMedia/Math"',
			 	'https://packagist.org/packages/ceus-media/math'
			) );
		$sign	= ( $amount < 0 && $periods % 2 > 0 ) ? -1 : 1;
		$value	= pow( abs( $amount ), 1 / $periods );
		return $sign * $value;
	}