(548^2 - 26^2):574
(a^2 - b^2) = (a + b) * (a - b)
(548^2 - 26^2):574 = (548 + 26) * (548 - 26) : 574 =
= 574 * 522 : 574 = 522
sqrt(447^2 - 420^2) =
= sqrt((447 - 420)*(447 + 420)) =
= sqrt(27 * 887) = sqrt(3 * 9 * 3 * 289) = sqrt(81) * sqrt(289) = 9 * 17 =
= 153