4.
12 / (3√2 - √3) =
= 12*(3√2 + √3) / (3√2 - √3)(3√2 + √3) =
= 12*(3√2 + √3) / ((3√2)²- (√3)²) =
= 12*(3√2 + √3) / (18 - 3) =
= 12*(3√2 + √3) / 15 =
= 4*(3√2 + √3) / 5,
(3√2 - 2√3) / (3√2 + 2√3) =
= (3√2 - 2√3) / (3√2 - 2√3) / (3√2 + 2√3) / (3√2 - 2√3) =
= (3√2 - 2√3)² / ((3√2)² - (2√3)²) =
= (9*2 - 2*3√2*2√3 + 4*3) / (9*2 - 4*3) =
= (18 - 12√6 + 12) / (18 - 12) =
= (30 - 12√6) / 6 =
= 6*(5 - 2√6) / 6 =
= 5 - 2√6