Câu a : Bạn áp dụng quy tắc khai phương mà làm : \(\sqrt{A.B}=\sqrt{A}.\sqrt{B}\) b) \(\sqrt{320.45}=\sqrt{64.5.5.9}=\sqrt{64.25.9}=\sqrt{64}.\sqrt{25}.\sqrt{9}=8.5.3=120\) c) và d) tương tự câu b) e) \(\sqrt{0,87.49+0,82.49}=\sqrt{49.\left(0,87.0,82\right)}=\sqrt{49.1,69}=\sqrt{49}.\sqrt{1,69}=7.1,3=9,1\) f) \(\sqrt{3^2.\left(-7\right)^2}=\sqrt{3^2}.\sqrt{\left(-7\right)^2}=3.\left|-7\right|=3.7=21\) g) \(\sqrt{27.48.\left(1-a\right)^2}=\sqrt{9.3.3.16.\left(1-a\right)^2}=\sqrt{81}.\sqrt{16}.\sqrt{\left(1-a\right)^2}=9.4.\left|1-a\right|\) Vì a > 1 nên => | 1- a| = a-1 Vậy : \(\sqrt{27.48.\left(1-a\right)^2}=9.4.\left(a-1\right)=36\left(a-1\right)\) h) \(\sqrt{a^4.\left(3-a\right)^2}=\left|a^2\right|.\left|3-a\right|\) Vì a2 > 0 nên => | a2 | = a2 Vì a \(\ge3\) nên => | 3-a| = a - 3 Vậy : \(\sqrt{a^4.\left(3-a\right)^2}=a^2.\left(a-3\right)\)Câu trả lời: Câu a : Bạn áp dụng quy tắc khai phương mà làm : \(\sqrt{A.B}=\sqrt{A}.\sqrt{B}\) b) \(\sqrt{320.45}=\sqrt{64.5.5.9}=\sqrt{64.25.9}=\sqrt{64}.\sqrt{25}.\sqrt{9}=8.5.3=120\) c) và d) tương tự câu b) e) \(\sqrt{0,87.49+0,82.49}=\sqrt{49.\left(0,87.0,82\right)}=\sqrt{49.1,69}=\sqrt{49}.\sqrt{1,69}=7.1,3=9,1\) f) \(\sqrt{3^2.\left(-7\right)^2}=\sqrt{3^2}.\sqrt{\left(-7\right)^2}=3.\left|-7\right|=3.7=21\) g) \(\sqrt{27.48.\left(1-a\right)^2}=\sqrt{9.3.3.16.\left(1-a\right)^2}=\sqrt{81}.\sqrt{16}.\sqrt{\left(1-a\right)^2}=9.4.\left|1-a\right|\) Vì a > 1 nên => | 1- a| = a-1 Vậy : \(\sqrt{27.48.\left(1-a\right)^2}=9.4.\left(a-1\right)=36\left(a-1\right)\) h) \(\sqrt{a^4.\left(3-a\right)^2}=\left|a^2\right|.\left|3-a\right|\) Vì a2 > 0 nên => | a2 | = a2 Vì a \(\ge3\) nên => | 3-a| = a - 3 Vậy : \(\sqrt{a^4.\left(3-a\right)^2}=a^2.\left(a-3\right)\)