Bài 28 (Trang 18 SGK Toán 9, Tập 1):

Tính:

a) $\sqrt{\frac{289}{225}}$;                    b)$\sqrt{2\frac{14}{25}}$;                   c)$\sqrt{\frac{0,25}{9}}$;                         d)$\sqrt{\frac{8,1}{1,6}}$;

Hướng dẫn giải:

a)$\sqrt{\frac{289}{225}}= \frac{\sqrt{289}}{\sqrt{225}}=\frac{\sqrt{{17}^2}}{\sqrt{{15}^2}}= \frac{17}{15}=1\frac{2}{15}$

b)$\sqrt{2\frac{14}{25}}= \sqrt{\frac{64}{25}}=\frac{\sqrt{64}}{\sqrt{25}}=\frac{\sqrt{8^2}}{\sqrt{5^2}}= \frac{8}{5}=1\frac{3}{5}$

c) $\sqrt{\frac{0,25}{9}}= \sqrt{\frac{25}{900}}=\frac{\sqrt{25}}{\sqrt{900}}=\frac{5}{30} =\frac{1}{6}$

d)$\sqrt{\frac{8,1}{1,6}}= \sqrt{\frac{81}{16}}=\frac{\sqrt{81}}{\sqrt{16}}=\frac{9}{4}$