수식 6: left parenthesis, "x" Subscript, 1 , Baseline plus "t" left parenthesis, "y" Subscript, 1 , Baseline minus "x" Subscript, 1 , Baseline , right parenthesis , "y" Subscript, 1 , Baseline plus "t" left parenthesis, "x" Subscript, 1 , Baseline minus "y" Subscript, 1 , Baseline , right parenthesis , right parenthesisx1+ty1−x1,y1+tx1−y1