Помогите пожалуйста 0,4*корень2500-1/5корень36= корень7^2-3^2= корень 0,81-36=...

$0.4 \times \sqrt{2500} - \frac{1}{5} \sqrt{36} = \\ 0.4 \times 50 - \frac{1}{5} \times 4 =$

$2 - \frac{4}{5} = 2 - 0.8 = 1.2$

$\sqrt{7 {}^{2} - {3}^{2} } = \sqrt{49 - 9} = \sqrt{40} = \\ \sqrt{10 \times 4} = 2 \sqrt{10}$

$\sqrt{0.81 - 36} = 0.9 - 6 = - 5.1$

$\ \sqrt{14} \times \sqrt{72} - \frac{ \sqrt{42} }{7} = \\ \sqrt{2 \times 7} \times \sqrt{36 \times 2} - \sqrt{6} =$

$\sqrt{2 \times 7} \times 6 \sqrt{2} - \sqrt{6} = \\ 6 \times \sqrt{2} \times \sqrt{2} \times \sqrt{7} - \sqrt{6} = \\ 12 \sqrt{7} - \sqrt{6}$

Последний не знаю