## moi nguoi lam giup em may cau nay voi a

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moi nguoi lam giup em may cau nay voi a

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1 year 2020-11-11T13:43:04+00:00 2 Answers 58 views 0

1. a.

\sqrt{125} – 4\sqrt{45} + 3\sqrt{20} – \sqrt{80}

=\sqrt{25*5} – 4\sqrt{9*5} + 3\sqrt{4*5} – \sqrt{16*5}

=5\sqrt{5} – 4*3\sqrt{5} + 3*2\sqrt{5} – 4\sqrt{5}

=5\sqrt{5} – 12\sqrt{5} + 6\sqrt{5} – 4\sqrt{5}

=-5\sqrt{5}

b.

(\sqrt{99}-\sqrt{18}-\sqrt{11})\sqrt{11}+3\sqrt{22}

=(\sqrt{9*11}-\sqrt{18}-\sqrt{11})\sqrt{11}+3\sqrt{22}

=(3\sqrt{11}-\sqrt{11}-\sqrt{18})\sqrt{11}+3\sqrt{22}

=(2\sqrt{11}-\sqrt{18})\sqrt{11}+3\sqrt{22}

=2\sqrt{11}\sqrt{11}-\sqrt{18}\sqrt{11}+3\sqrt{22}

=22-3\sqrt{22}+3\sqrt{22}

=22

c.

2\sqrt{\frac{27}{4}}-\sqrt{\frac{48}{9}}-2/5\sqrt{\frac{75}{16}}

=2/2\sqrt{27}-1/3\sqrt{48}-2/20\sqrt{75}

=\sqrt{27}-1/3\sqrt{48}-1/10\sqrt{75}

=3\sqrt{3}-1/3*4\sqrt{3}-1/10*5\sqrt{3}

=3\sqrt{3}-4/3\sqrt{3}-1/2\sqrt{3}

=7/6\sqrt{3}

d.

=3\sqrt{9/8}-\sqrt{49/2}+\sqrt{25/18}

=3*3\sqrt{1/8}-7\sqrt{1/2}+5\sqrt{1/18}

=9\sqrt{1/8}-7\sqrt{1/2}+5\sqrt{1/18}

=9*1/2\sqrt{1/2}-7\sqrt{1/2}+5*1/3\sqrt{1/2}

=9/2\sqrt{1/2}-7\sqrt{1/2}+5/3\sqrt{1/2}

=-5/6\sqrt{1/2}

e.

(1+(5-\sqrt{5})/(1-\sqrt{5}))((5+\sqrt{5})/(1+\sqrt{5})+1)

=(1+((5-\sqrt{5})(1+\sqrt{5}))/((1-\sqrt{5})(1+\sqrt{5})))(((1-\sqrt{5})(5+\sqrt{5}))/((1-\sqrt{5})(1+\sqrt{5}))+1)

=(1+((5-\sqrt{5})(1+\sqrt{5}))/(1-(\sqrt{5})^2))(((1-\sqrt{5})(5+\sqrt{5}))/(1-(\sqrt{5})^2)+1)

=(1+((5-\sqrt{5})(1+\sqrt{5}))/(1-5))(((1-\sqrt{5})(5+\sqrt{5}))/(1-5)+1)

=(1+(5+5\sqrt{5}-\sqrt{5}-5)/(-4))((5-5\sqrt{5}+\sqrt{5}-5)/(-4)+1)

=(1+(-4\sqrt{5})/(4))((-4\sqrt{5})/(-4)+1)

=[1+(-\sqrt{5})](\sqrt{5}+1)

=(1-\sqrt{5})(1+\sqrt{5})

=1-(\sqrt{5})^2

=1-5

=-4

f.

1/(\sqrt{3}-\sqrt{2})+1/(\sqrt{3}+\sqrt{2})

=(\sqrt{3}+\sqrt{2})/((\sqrt{3}-\sqrt{2})(\sqrt{3}+\sqrt{2}))+(\sqrt{3}-\sqrt{2})/((\sqrt{3}-\sqrt{2})(\sqrt{3}+\sqrt{2}))

=(\sqrt{3}+\sqrt{2})/((\sqrt{3})^2-(\sqrt{2})^2)+(\sqrt{3}-\sqrt{2})/((\sqrt{3})^2-(\sqrt{2})^2)

=(\sqrt{3}+\sqrt{2})/(3-2)+(\sqrt{3}-\sqrt{2})/(3-2)

=\sqrt{3}+\sqrt{2}+\sqrt{3}-\sqrt{2}

=2\sqrt{3}

2. Đáp án:

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