(√7 + (√2 - 1))(√7 - (√2 - 1)) = [(a-b)(a+b) = a² - b²] = (√7)² - (√2 - 1)² =
=7 - (2 + 1 - 2√2) = 7 - 3 + 2√2 = 4 + 2√2