Tính (a) căn (4/25) (b) −căn(3^2)

a) \[\sqrt {\frac{4}{{25}}} = \sqrt {\frac{{{2^2}}}{{{5^2}}}} = \frac{2}{5}\]

b) \[ - \sqrt {{3^2}} = - \left( {\sqrt {{3^2}} } \right) = - 3\]

c) \[ - \sqrt {{{\left( { - 6} \right)}^2}} = - \sqrt {{6^2}} = - 6\]

d) \[{\left( { - \sqrt 7 } \right)^2} = {\left( { - 1} \right)^2}.{\left( {\sqrt 7 } \right)^2} = 1.7 = 7\]