Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
\(A=\sqrt{3+\sqrt{5}}.\sqrt{3-\sqrt{5}}=\sqrt{3^2-\left(\sqrt{5}\right)^2}=\sqrt{4}=2\)
\(B=\sqrt{150.27.96}=\sqrt{150}.\sqrt{27}.\sqrt{96}=5\sqrt{6}.3\sqrt{3}.4\sqrt{6}=360\sqrt{3}\)
\(C=\left(\sqrt{27}+\sqrt{48}\right)^2-\left(\sqrt{27}-\sqrt{48}\right)^2\)\(=\left[\left(\sqrt{27}+\sqrt{48}-\sqrt{27}+\sqrt{48}\right)\left(\sqrt{27}+\sqrt{48}+\sqrt{27}-\sqrt{48}\right)\right]\)
\(=2\sqrt{27}.2\sqrt{48}=2.3\sqrt{3}.2.4\sqrt{3}=144\)
\(D=\sqrt{137^2-88^2}-\sqrt{192^2-111^2}=\sqrt{\left(137+88\right)\left(137-88\right)}-\sqrt{\left(192+111\right)\left(192-111\right)}\)
\(=\sqrt{225.49}-\sqrt{303.81}=15.7-9.\sqrt{303}=9\left(\frac{35}{3}-\sqrt{303}\right)\)
\(E=\sqrt{\frac{225}{4}.\frac{81}{25}.\frac{49}{64}}=\frac{15}{2}.\frac{9}{5}.\frac{7}{8}=\frac{189}{16}\)
\(F=\sqrt{\frac{27}{25}}.\sqrt{\frac{49}{189}}.\sqrt{\frac{700}{99}}=\frac{3\sqrt{3}}{5}.\frac{7}{3\sqrt{21`}}.\frac{10\sqrt{7}}{3\sqrt{11}}=\frac{14}{3\sqrt{11}}\)
\(H=\sqrt{105}.\left[\sqrt{\frac{15}{7}}-\sqrt{\frac{35}{5}}+\sqrt{\frac{21}{5}}\right]=\sqrt{105}.\left[\sqrt{\frac{15}{7}}-\sqrt{7}+\sqrt{\frac{21}{5}}\right]\)
\(=\sqrt{105}.\left[\frac{\sqrt{75}-\sqrt{49}+\sqrt{147}}{\sqrt{35}}\right]=\sqrt{3}\left(12\sqrt{3}-7\right)=36-7\sqrt{3}\)
\(K=\sqrt{64.14.21.54}-\sqrt{35.45.12}=8.\sqrt{14}.\sqrt{21}.3\sqrt{6}-\sqrt{35}.3\sqrt{5}.2\sqrt{3}\)
\(=24.\sqrt{14.21.6}-6\sqrt{35.5.3}=24.42-30\sqrt{21}=30\left(\frac{168}{5}-\sqrt{21}\right)\)
đặt A=...
ta có
A=\(\frac{\sqrt{2}-1}{2-1}+\frac{\sqrt{3}-\sqrt{2}}{3-2}+...+\frac{\sqrt{100}-\sqrt{99}}{100-99}\)
=\(\sqrt{2}-1+\sqrt{3}-\sqrt{2}+...+\sqrt{100}-\sqrt{99}=\sqrt{100}-1=10-1=9\)
Ta có:
\(\frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+.....+\frac{1}{\sqrt{n-1}+\sqrt{n}}=\sqrt{n}-1\)
Lại có:
\(\frac{1}{\sqrt{x}+\sqrt{x-1}}=\frac{\sqrt{x}-\sqrt{x-1}}{\left(\sqrt{x}+\sqrt{x-1}\right)\left(\sqrt{x}-\sqrt{x-1}\right)}=\sqrt{x}-\sqrt{x-1}\)
Do đó:
\(A=\frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+....+\frac{1}{\sqrt{99}+\sqrt{100}}\)
\(\Leftrightarrow\sqrt{1}-\sqrt{2}+\sqrt{2}-\sqrt{3}+....+\sqrt{99}-\sqrt{100}\)
\(\Leftrightarrow\sqrt{100}-1=10-1=9\)
b/ Ta có: \(\frac{1}{\left(n+1\right)\sqrt{n}+n\sqrt{n+1}}=\frac{1}{\sqrt{n}.\sqrt{n+1}.\left(\sqrt{n+1}+\sqrt{n}\right)}\)
\(=\frac{\sqrt{n+1}-\sqrt{n}}{\sqrt{n+1}.\sqrt{n}}=\frac{1}{\sqrt{n}}-\frac{1}{\sqrt{n+1}}\)
Áp dụng vào bài toán ta được
\(\frac{1}{2\sqrt{1}+1\sqrt{2}}+\frac{1}{3\sqrt{2}+2\sqrt{3}}+...+\frac{1}{100\sqrt{99}+99\sqrt{100}}\)
\(=\frac{1}{\sqrt{1}}-\frac{1}{\sqrt{2}}+\frac{1}{\sqrt{2}}-\frac{1}{\sqrt{3}}+...+\frac{1}{99}-\frac{1}{\sqrt{100}}\)
\(=\frac{1}{\sqrt{1}}-\frac{1}{\sqrt{100}}=1-\frac{1}{10}=\frac{9}{10}\)
Cả 2 câu là n tự nhiên khác 0 hết nhé
a/ Ta có: \(\frac{1}{\sqrt{n}+\sqrt{n+1}}=\frac{\sqrt{n+1}-\sqrt{n}}{n+1-n}=\sqrt{n+1}-\sqrt{n}\)
Áp đụng vào bài toán được
\(\frac{1}{\sqrt{1}+\sqrt{2}}+\frac{1}{\sqrt{2}+\sqrt{3}}+...+\frac{1}{\sqrt{1680}+\sqrt{1681}}\)
\(=\sqrt{2}-\sqrt{1}+\sqrt{3}-\sqrt{2}+...+\sqrt{1681}-\sqrt{1680}\)
\(=\sqrt{1681}-\sqrt{1}=41-1=40\)
\(\left(\sqrt{4,5}-\frac{1}{2}.\sqrt{72}+5\sqrt{\frac{1}{2}}\right).\left(42\sqrt{\frac{25}{6}}-10\sqrt{\frac{3}{2}}-12\sqrt{\frac{98}{3}}\right)\)
=\(\left(\frac{3\sqrt{2}}{2}-3\sqrt{2}+\frac{5\sqrt{2}}{2}\right).\left(35\sqrt{6}-5\sqrt{6}-28\sqrt{6}\right)\)
=\(\left(\frac{3\sqrt{2}-6\sqrt{2}+5\sqrt{2}}{2}\right).2\sqrt{6}\)
=\(2\sqrt{2}.\sqrt{6}=4\sqrt{3}\)
a/ Đề sai
b/ \(\sqrt{125}-4\sqrt{45}+3\sqrt{2}-\sqrt{80}=5\sqrt{5}-12\sqrt{5}+3\sqrt{2}-4\sqrt{5}\)
\(=-11\sqrt{5}+3\sqrt{2}\)
c/ \(2\sqrt{\frac{27}{4}}-\sqrt{\frac{48}{9}}-\frac{2}{5}\sqrt{\frac{75}{16}}=2.\frac{3\sqrt{3}}{2}-\frac{4\sqrt{3}}{3}-\frac{2}{5}.\frac{5\sqrt{3}}{4}\)
\(=3\sqrt{3}-\frac{4\sqrt{3}}{3}-\frac{\sqrt{3}}{2}=\sqrt{3}\left(3-\frac{4}{3}-\frac{1}{2}\right)=\frac{7\sqrt{3}}{6}\)
d/ \(\left(\sqrt{99}-\sqrt{18}-\sqrt{11}\right)\cdot\sqrt{11}+3\sqrt{22}=33-3\sqrt{22}-11+3\sqrt{22}=22\)
\(=\frac{2-1}{\sqrt{2}+1}+\frac{3-2}{\sqrt{3}+\sqrt{2}}+\frac{4-3}{\sqrt{4}+\sqrt{3}}+...+\frac{100-99}{\sqrt{100}+\sqrt{99}}.\)
\(=\frac{\left(\sqrt{2}+1\right)\left(\sqrt{2}-1\right)}{\sqrt{2}+1}+\frac{\left(\sqrt{3}+\sqrt{2}\right)\left(\sqrt{3}-\sqrt{2}\right)}{\sqrt{3}+\sqrt{2}}+\frac{\left(\sqrt{4}+\sqrt{3}\right)\left(\sqrt{4}-\sqrt{3}\right)}{\sqrt{4}+\sqrt{3}}+...\)
\(=\sqrt{2}-1+\sqrt{3}-\sqrt{2}+\sqrt{4}-\sqrt{3}+...+\sqrt{100}-\sqrt{99}\)
\(=\sqrt{100}-1=10-1=9.\)
\(\sqrt{\frac{27}{25}}.\sqrt{\frac{44}{189}}.\sqrt{\frac{700}{99}}\)
\(=\sqrt{\frac{27}{25}.\frac{44}{189}.\frac{700}{99}}\)
\(=\sqrt{\frac{16}{9}}\)
\(=\frac{4}{3}\)
học tốt