public function buildExpressions()
	{
		$this->expressions	= array();
		$values	= array_keys( $this->data );
		for( $i=0; $i<count( $values ); $i++ )
		{
			$this->expressions[$i]	= "";
			for( $k=0; $k<count( $values ) ;$k++ )
			{
				if( $k == $i )
					continue;
				$expression	= "(x-".$values[$k].")/(".$values[$i]."-".$values[$k].")";
				if( strlen( $this->expressions[$i] ) )
					$this->expressions[$i]	.= "*".$expression;
				else
					$this->expressions[$i]	= $expression;
			}
		}
	}