Question

a) Tính \(\sqrt{3}.\sqrt{75}\);

b) Rút gọn \(\sqrt{5ab^3}.\sqrt{5ab}\) (với a < 0, b < 0)

Answer 1

a) Ta có: \(\sqrt 3 .\sqrt {75}  = \sqrt {3.75}  = \sqrt {225}  = 15\)

b) \(\sqrt {5a{b^3}} .\sqrt {5ab}  \) \(= \sqrt {5a{b^3}.5ab}  \) \(= \sqrt {25a^2{b^4}} \) \(= \sqrt {25}. \sqrt{a^2} \sqrt{b^4} \) \(= 5\left| a \right| \left| {b^2} \right| \) \(= 5(-a)b^2 \) \(= -5ab^2\)