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a) \(\sqrt{75}+\sqrt{48}-\sqrt{300}\) = \(5\sqrt{3}+4\sqrt{3}-10\sqrt{3}\) = \(-\sqrt{3}\)
b) \(\sqrt{98}-\sqrt{72}+0,5\sqrt{8}\) = \(7\sqrt{2}-6\sqrt{2}+\sqrt{2}\) = \(2\sqrt{2}\)
c) \(\sqrt{9a}-\sqrt{16a}+\sqrt{49a}\) = \(3\sqrt{a}-4\sqrt{a}+7\sqrt{a}\) = \(6\sqrt{a}\)
d) \(\sqrt{16b}+2\sqrt{40b}-3\sqrt{90b}\) = \(4\sqrt{b}+4\sqrt{10b}-9\sqrt{10b}\)
= \(4\sqrt{b}-5\sqrt{10b}\)
\(\sqrt{20}-\sqrt{45}+3\sqrt{18}+\sqrt{72}\)
\(=\sqrt{4.5}-\sqrt{9.5}+3\sqrt{18}+\sqrt{4.18}\)
\(=2\sqrt{5}-3\sqrt{5}+3\sqrt{18}+2\sqrt{18}\)
\(=-\sqrt{5}+5\sqrt{18}\)
Với x > 0
\(P=\frac{\sqrt{a}+5}{a+5\sqrt{a}}=\frac{\sqrt{a}+5}{\sqrt{a}\left(\sqrt{a}+5\right)}=\frac{1}{\sqrt{a}}=\frac{\sqrt{a}}{a}\)
\(\sqrt{8-2\sqrt{5}}=\sqrt{5-2\sqrt{5}.\sqrt{3}+3}=\sqrt{\left(\sqrt{5}-\sqrt{3}\right)^2}=\sqrt{5}-\sqrt{3}\)
b) \(\sqrt{16x}-5\left(\sqrt{x}-2\right)-\sqrt{79x}-5\)
\(=\sqrt{4^2x}-5\sqrt{x}+10-\sqrt{79x}-5\)
\(=4\sqrt{x}-5\sqrt{x}-\sqrt{79x}+5\)
\(=-\sqrt{x}-\sqrt{79x}+5\)
\(=-\sqrt{x}-\sqrt{79}.\sqrt{x}+5\)
\(=\sqrt{x}\left(-1-\sqrt{79}\right)+5\)
\(a.A=\sqrt{75}+\sqrt{48}-\sqrt{300}=\sqrt{25.3}+\sqrt{16.3}-\sqrt{100.3}=5\sqrt{3}+4\sqrt{3}-10\sqrt{3}=-\sqrt{3}\) \(b.B=\sqrt{98}-\sqrt{72}+0,5\sqrt{8}=\sqrt{49.2}-\sqrt{36.2}+0,5\sqrt{4.2}=7\sqrt{2}-6\sqrt{2}+\sqrt{2}=2\sqrt{2}\) \(c.\dfrac{5\sqrt{5}-\sqrt{15.5}+5\sqrt{5}}{\sqrt{5}}=\dfrac{\sqrt{5}\left(10-\sqrt{15}\right)}{\sqrt{5}}=10-\sqrt{15}\)
\(\left(\sqrt{3}-\sqrt{2}\right)\sqrt{5+2\sqrt{6}}\)
\(=\sqrt{15+2.3.\sqrt{6}}\)\(-\sqrt{10+2.2\sqrt{6}}\)
\(=\sqrt{9+2.3\sqrt{6}+6}\)\(-\sqrt{6+2.\sqrt{6}.2+4}\)
\(=\sqrt{\left(3+\sqrt{6}\right)^2}\)\(-\sqrt{\left(\sqrt{6}+2\right)^2}\)
\(=3+\sqrt{6}\)\(-2\)\(-\sqrt{6}=\left(3-2\right)+\left(\sqrt{6}-\sqrt{6}\right)\)
\(=1+0=1\)
a) \((\sqrt{3}-\sqrt{2}).\sqrt{(\sqrt{3}+\sqrt{2})^2}\)
\(\left(\sqrt{3}-\sqrt{2}\right).\left(\sqrt{3}+\sqrt{2}\right)\)
\(\left(\sqrt{3}\right)^2-\left(\sqrt{2}\right)^2\)\(=3-2=1\)
b) \(\sqrt{24+8\sqrt{5}}+\sqrt{9-4\sqrt{5}}\)
=\(\sqrt{(2+2\sqrt{5})^2}+\sqrt{(\sqrt{5}-2)^2}\)
=\(2+2\sqrt{5}+\sqrt{5}-2\)\(=3\sqrt{5}\)
Quy đồng khử mẫu bằng cách nhân với biểu thức để cho mẫu mất căn thức
