a² - b² = (a - b)(a + b)(30² - 28²)/116 + 30*28 = (30 - 28)(30+ 28)/2*58 + 30*28 = 2*58 / 2*58 + 30*(30 - 2) = 1 + 900 - 60 = 841
a² - b² = (a - b)(a + b)
(30² - 28²)/116 + 30*28 = (30 - 28)(30+ 28)/2*58 + 30*28 = 2*58 / 2*58 + 30*(30 - 2) = 1 + 900 - 60 = 841