72. Найдите значение выражения: 1) (√6)² - 1,69; 2) (2√7)² - (5√2)²; 3) 18 · (-1/3 √5)² - (1/6) · (4√3)²; 4) √961 - (1/5 √125)².

1.

\((\sqrt{6})^2 - 1.69 = 6 - 1.69 = 4.31\)

2.

\((2\sqrt{7})^2 - (5\sqrt{2})^2 = (4 \cdot 7) - (25 \cdot 2) = 28 - 50 = -22\)

3.

\(18 \cdot \left(-\frac{1}{3}\sqrt{5}\right)^2 - \frac{1}{6} \cdot (4\sqrt{3})^2 = 18 \cdot \left(\frac{1}{9} \cdot 5\right) - \frac{1}{6} \cdot (16 \cdot 3) = 18 \cdot \frac{5}{9} - \frac{1}{6} \cdot 48 = 2 \cdot 5 - 8 = 10 - 8 = 2\)

4.

\(\sqrt{961} - \left(\frac{1}{5}\sqrt{125}\right)^2 = 31 - \left(\frac{1}{5} \cdot 5\sqrt{5}\right)^2 = 31 - (\sqrt{5})^2 = 31 - 5 = 26\)