b: \(=\dfrac{1}{13}\left(\dfrac{10}{9}+\dfrac{27}{11}\right)+\dfrac{11}{13}=\dfrac{1}{13}\cdot\dfrac{353}{99}+\dfrac{11}{13}=\dfrac{1442}{1287}\)

c: \(=\dfrac{-5}{7}\left(\dfrac{3}{11}+\dfrac{8}{11}\right)+\dfrac{9}{7}=\dfrac{-5}{7}+\dfrac{9}{7}=\dfrac{4}{7}\)

d: \(=\dfrac{-5}{-5}\cdot\dfrac{13}{13}\cdot\dfrac{5}{9}\cdot\left(-18\right)=\dfrac{5}{9}\cdot\left(-18\right)=-10\)

a) \(\dfrac{\sqrt{15}+\sqrt{21}}{\sqrt{5}+\sqrt{7}}=\dfrac{\sqrt{3}.\sqrt{5}+\sqrt{3}.\sqrt{7}}{\sqrt{5}.\sqrt{7}}=\dfrac{\sqrt{3}\left(\sqrt{5}.\sqrt{7}\right)}{\sqrt{5}.\sqrt{7}}=\sqrt{3}\)

a) \(\dfrac{\sqrt{15}+\sqrt{21}}{\sqrt{5}+\sqrt{7}}=\dfrac{\sqrt{3}\left(\sqrt{5}+\sqrt{7}\right)}{\sqrt{5}+\sqrt{7}}=\sqrt{3}\)

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\(b,=\left(x-4\right)^2\\ c,=x^2-25\\ d,=\left(x+4\right)^3\\ e,=\left(x-2\right)^3\\ f,=x^3+8\\ g,=x^3-27\\ i,=\left(x-1\right)\left(x+1\right)\\ l,=\left(2x-3\right)\left(2x+3\right)\\ m,=\left(4x-1\right)^2\\ p,=\left(x+3\right)\left(x^2-3x+9\right)\)

1 which

2 who 

3 0

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Chọn A

3:

Bước 1: Chọn ô

Bước 2: Nhập dấu '='

Bước 3: Gõ công thức

Bước 4: Nhấn enter