в) $$\sqrt{90} \cdot \frac{\sqrt{5}}{\sqrt{2}}$$; г) $$\sqrt{1\frac{1}{5}} \div \sqrt{\frac{6}{7}} \cdot \sqrt{\frac{5}{7}}$$.

в) $$\sqrt{90} \cdot \frac{\sqrt{5}}{\sqrt{2}} = \sqrt{\frac{90 \cdot 5}{2}} = \sqrt{45 \cdot 5} = \sqrt{9 \cdot 5 \cdot 5} = \sqrt{9} \cdot \sqrt{5^2} = 3 \cdot 5 = 15$$ г) $$\sqrt{1\frac{1}{5}} \div \sqrt{\frac{6}{7}} \cdot \sqrt{\frac{5}{7}} = \sqrt{\frac{6}{5}} \div \sqrt{\frac{6}{7}} \cdot \sqrt{\frac{5}{7}} = \sqrt{\frac{6}{5} \div \frac{6}{7} \cdot \frac{5}{7}} = \sqrt{\frac{6}{5} \cdot \frac{7}{6} \cdot \frac{5}{7}} = \sqrt{\frac{6 \cdot 7 \cdot 5}{5 \cdot 6 \cdot 7}} = \sqrt{1} = 1$$