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a: Ta có: \(\dfrac{4}{\sqrt{7}-\sqrt{3}}+\dfrac{6}{3+\sqrt{3}}+\dfrac{\sqrt{7}-7}{\sqrt{7}-1}\)
\(=\sqrt{7}+\sqrt{3}+3-\sqrt{3}-\sqrt{7}\)
=3
\(A=3\sqrt{2}+5\sqrt{8}-2\sqrt{50}\)
\(=3\sqrt{2}+10\sqrt{2}-10\sqrt{2}\)
\(=3\sqrt{2}\)
1) \(x+5\sqrt{x}+6=x+2\sqrt{x}+3\sqrt{x}+6\)
\(=\sqrt{x}\left(\sqrt{x}+2\right)+3\left(\sqrt{x}+2\right)\)
\(=\left(\sqrt{x}+2\right)\left(\sqrt{x}+3\right)\)
2) \(=\left(4\sqrt{3}+3\sqrt{15}-12\sqrt{15}\right)\sqrt{3}\)
\(=\left(4\sqrt{3}-8\sqrt{15}\right)\sqrt{3}=12-24\sqrt{5}\)
b: Ta có: \(4\sqrt{5}=\sqrt{4^2\cdot5}=\sqrt{80}\)
\(5\sqrt{3}=\sqrt{5^2\cdot3}=\sqrt{75}\)
mà 80>75
nên \(4\sqrt{5}>5\sqrt{3}\)
\(A=15+12+4\sqrt{45}+12\sqrt{5}=27+24\sqrt{5}\)
\(B=\left(2\sqrt{3}+6\sqrt{3}\right).\frac{\sqrt{3}}{2}-5\sqrt{6}=\frac{8\sqrt{3}.\sqrt{3}}{2}-5\sqrt{6}=12-5\sqrt{6}\)
\(C=4\sqrt{3}+\frac{4}{\sqrt{3}}+10\sqrt{5}-\frac{10}{\sqrt{5}}=\frac{16}{\sqrt{3}}+8\sqrt{5}\)
\(20\sqrt{40\sqrt{12}}-2\sqrt{\sqrt{75}}-3\sqrt{5\sqrt{48}}\)
\(=20\sqrt{80\sqrt{3}}-2\sqrt{5\sqrt{3}}-2\sqrt{20\sqrt{3}}\)
\(=80\sqrt{5\sqrt{3}}-2\sqrt{5\sqrt{3}}-6\sqrt{5\sqrt{3}}=72\sqrt{5\sqrt{3}}\)
BT=\(\dfrac{2\left(\sqrt{3}-1\right)}{\left(\sqrt{3}+1\right)\left(\sqrt{3}-1\right)}+\dfrac{2+\sqrt{3}}{\left(2-\sqrt{3}\right)\left(2+\sqrt{3}\right)}+\dfrac{12\left(3-\sqrt{3}\right)}{\left(\sqrt{3}+3\right)\left(3-\sqrt{3}\right)}\)
\(=\dfrac{2\left(\sqrt{3}-1\right)}{2}+\dfrac{2+\sqrt{3}}{4-3}+\dfrac{12\left(3-\sqrt{3}\right)}{9-3}\)
\(=\sqrt{3}-1+2+\sqrt{3}+2\left(3-\sqrt{3}\right)\)
\(=\sqrt{3}-1+2+\sqrt{3}+6-2\sqrt{3}=7\)