b)  63 y 3 7 y với y > 0

=  63 y 3 7 y = 9 y 2 = 3 y = 3 y do y > 0

a: \(\sqrt{48a^4b^2}=\sqrt{16a^4b^2\cdot3}=4\sqrt{3}\cdot a^2\cdot\left|b\right|\)

\(=-4\sqrt{3}\cdot a^2b\)

b: \(\sqrt{-25x^3}=\sqrt{-25x^2\cdot x}=\left|25x^2\right|\cdot\sqrt{-x}\)

\(=-5x\sqrt{-x}\)

8 y 2 = 4 . 2 y 2 = 2 y 2 = - 2 y 2 ( với y < 0 )

25 x 3 = 25 x 2 . x = 5 x x = 5 x x ( với x > 0 )

7 x 2 = x 7 = x 7 ( với x > 0 )

\(\sqrt{\left(-9\right)\cdot\left(-36\right)\cdot ab^2}\)

\(=\sqrt{9\cdot36\cdot ab^2}\)

\(=3\cdot4\cdot\left|b\right|\cdot\sqrt{a}\)

\(=12\left|b\right|\cdot\sqrt{a}\)

a) \(2\sqrt{5a^2}=2\sqrt{5}\left|a\right|=-2a\sqrt{5}\)

b)\(2\sqrt{18a^2}=2.3\sqrt{2}.\left|a\right|=6a\sqrt{2}\)

c)\(\sqrt{-9b^3}=\sqrt{9.\left(-b\right)^3}=3\sqrt{-b}.\left|b\right|=-3b\sqrt{-b}\)

d)\(\sqrt{24a^4b^8}=\sqrt{6.\left(4a^2b^4\right)^2}=2a^2b^4\sqrt{6}\)

a: \(\sqrt{5a^2}=\left|a\sqrt{5}\right|=-a\sqrt{5}\left(a< =0\right)\)

c: A=\(\sqrt{72a^2b^4}=\sqrt{36a^2b^4\cdot2}=6\sqrt{2}\cdot b^2\cdot\left|a\right|\)

mà a<0

nên \(A=-6\sqrt{2}\cdot ab^2\)

d: \(\sqrt{24a^4b^8}=\sqrt{4a^4b^8\cdot6}=2a^2b^4\cdot\sqrt{6}\)