\(\sqrt{8}+\sqrt{14}< \sqrt{9}+\sqrt{16}=3+4=7\)

\(\sqrt{66}-1>\sqrt{64}-1=8-1=7>\sqrt{8}+\sqrt{14}\)

a: \(\sqrt[3]{-8}\cdot\sqrt[3]{27}=-2\cdot3=-6\)

\(\sqrt[3]{\left(-8\right)\cdot27}=\sqrt[3]{-216}=-6\)

Do đó: \(\sqrt[3]{-8}\cdot\sqrt[3]{27}=\sqrt[3]{\left(-8\right)\cdot27}\)

b: \(\dfrac{\sqrt[3]{-8}}{\sqrt[3]{27}}=-\dfrac{2}{3}\)

\(\sqrt[3]{-\dfrac{8}{27}}=-\dfrac{2}{3}\)

Do đó: \(\dfrac{\sqrt[3]{-8}}{\sqrt[3]{27}}=\sqrt[3]{-\dfrac{8}{27}}\)

a: \(\left(\sqrt{21}-\sqrt{5}\right)^2=26-2\sqrt{105}\)

\(\left(\sqrt{20}-\sqrt{6}\right)^2=26-2\sqrt{120}\)

mà \(-2\sqrt{105}>-2\sqrt{120}\)

nên \(\sqrt{21}-\sqrt{5}>\sqrt{20}-\sqrt{6}\)

b: \(\left(\sqrt{2}+\sqrt{8}\right)^2=10+2\cdot4=16=12+4\)

\(\left(3+\sqrt{3}\right)^2=12+6\sqrt{3}\)

mà \(4< 6\sqrt{3}\)

nên \(\sqrt{2}+\sqrt{8}< 3+\sqrt{3}\)

\(A=\sqrt{12+\sqrt{12+\sqrt{12}}}+\sqrt{6+\sqrt{6+\sqrt{6+\sqrt{6}}}}< \sqrt{12+\sqrt{12+\sqrt{16}}}+\sqrt{6+\sqrt{6+\sqrt{6+\sqrt{9}}}}\)\(=7\)

\(B=\sqrt{14}+\sqrt{11}>\sqrt{13,69}+\sqrt{10,89}=7\)

\(\Rightarrow A< B\)

Ta có:

 \(12< 16\Rightarrow\sqrt{12}< \sqrt{16}=4\\ 6< 9\Rightarrow\sqrt{6}< \sqrt{9}=3\)

\(\Rightarrow A< \sqrt{12+\sqrt{12+4}}+\sqrt{6+\sqrt{6+\sqrt{6+3}}}=\sqrt{12+4}+\sqrt{6+3}=4+3=7\) (1)

Lại có :

\(B=\sqrt{14}+\sqrt{11}\Rightarrow B^2=25+2\sqrt{14.11}=25+2\sqrt{154}>25+2\sqrt{144}=25+2.12=49=7^2\)

Mà B > 0

\(\Rightarrow B>7\) (2)

Từ (1),(2) suy ra A<B

\(A=\dfrac{1}{\sqrt{12}+\sqrt{11}}\)

\(B=\dfrac{1}{\sqrt{14}+\sqrt{13}}\)

mà \(\sqrt{12}+\sqrt{11}< \sqrt{14}+\sqrt{13}\)

nên A>B

a)\(\sqrt{8}+3< \sqrt{9}+3=3+3=6< 6+\sqrt{2}\)

b)\(14=\sqrt{196}>\sqrt{195}=\sqrt{13.15}=\sqrt{13}.\sqrt{15}\)

c) Ta có: \(\hept{\begin{cases}\sqrt{27}>\sqrt{25}=5\\\sqrt{6}>\sqrt{4}=2\end{cases}\Rightarrow\sqrt{27}+\sqrt{6}+1>5+2+1=8}\)

Mà \(\sqrt{48}< \sqrt{49}=7< 8\)

\(\Rightarrow\sqrt{27}+\sqrt{6}+1>\sqrt{48}\)

Tham khảo nhé~

Đặt A = \(\sqrt{15}\)-\(\sqrt{14}\)và B = \(\sqrt{14}\)-\(\sqrt{13}\)(A, B >0)

A^2 = 29-2\(\sqrt{15.14}\) và B^2 = 27 -2\(\sqrt{14.13}\)

A^2-B^2 = 2-2(\(\sqrt{15.14}\)+\(\sqrt{14.13}\)) <0

=> A^2 < B^2 => A<B

\(Q=\sqrt[3]{20+14\sqrt{2}}+\sqrt[3]{20-14\sqrt{2}}\)

\(=\sqrt[3]{8+12\sqrt{2}+12+2\sqrt{2}}+\sqrt[3]{8-12\sqrt{2}+12-2\sqrt{2}}\)

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

\(=2+\sqrt{2}+2-\sqrt{2}=4\)

Làm tiếp nhé