Номер 670

1) √5(√5 + √20) = √5 · √5 + √5 · √20 = √52 + √100 = 5 + 10 = 15;

2) (5√2 – √18 + √50)√2 = (5√2 – 3√2 + 5√2)√2 = 7√2 · √2 = 7 · 2 = 14;

3) (1 – √2)(3 + √2) = 3 + √2 – 3√2 – √22 = 3 – 2√2 – 2 = 1 – 2√2;

4) (2 + √7)(1 – √7) = 2 – 2√7 + √7 – √7 · √7 = 2 – √7 – 7 = –√7 – 5.