[tex]a) \ \sqrt{1\dfrac{11}{25}}=\sqrt{\dfrac{25\cdot1+11}{25}}=\sqrt{\dfrac{36}{25}}=\sqrt{\dfrac{6^{2}}{5^{2}}}=\dfrac{6}{5}=1\dfrac{1}{5}[/tex]
[tex]Spr.\ 1\dfrac{1}{5}\cdot1\dfrac{1}{5}=\dfrac{6}{5}\cdot\dfrac{6}{5}=\dfrac{6\cdot6}{5\cdot5}=\dfrac{36}{25}=1\dfrac{11}{25}[/tex]
[tex]b) \ \sqrt{5\dfrac{4}{9}}=\sqrt{\dfrac{9\cdot5+4}{9}}=\sqrt{\dfrac{49}{9}}=\sqrt{\dfrac{7^{2}}{3^{2}}}=\dfrac{7}{3}=2\dfrac{1}{3}[/tex]
[tex]Spr.\ 2\dfrac{1}{3}\cdot2\dfrac{1}{3}=\dfrac{7}{3}\cdot\dfrac{7}{3}=\dfrac{7\cdot7}{3\cdot3}=\dfrac{49}{9}=5\dfrac{4}{9}[/tex]
[tex]c) \ \sqrt{3\dfrac{13}{36}}=\sqrt{\dfrac{36\cdot3+13}{36}}=\sqrt{\dfrac{121}{36}}=\sqrt{\dfrac{11^{2}}{6^{2}}}=\dfrac{11}{6}=1\dfrac{5}{6}[/tex]
[tex]Spr.\ 1\dfrac{5}{6}\cdot1\dfrac{5}{6}=\dfrac{11}{6}\cdot\dfrac{11}{6}=\dfrac{11\cdot11}{6\cdot6}=\dfrac{121}{36}=3\dfrac{13}{36}[/tex]