a) \(3\sqrt 5 = \sqrt {\left( {{3^3} \times 5} \right)} = \sqrt {45} \)
b) \(1,2\sqrt 5 = \sqrt {\left( {1,{2^2}.5} \right)} = \sqrt {7,2} \)
c) \(a{b^4}\sqrt a = \sqrt {\left( {{{\left( {a{b^4}} \right)}^2}a} \right)} \)\(= \sqrt {\left( {{a^2}{b^8}a} \right)} = \sqrt {{a^3}{b^8}} \)
d) \( - 2a{b^2}\sqrt 5 a = - \sqrt {\left( {{{\left( {2a{b^2}} \right)}^2} \times 5a} \right)} \)\( = - \sqrt {\left( {4{a^2}{b^4} \times 5a} \right)} = - \sqrt {20{a^3}{b^4}} \)
