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bài 1:
\(\frac{7}{4}\left(\frac{33}{42}+\frac{3333}{2020}+\frac{333333}{303030}+\frac{33333333}{42424242}\right)\)
\(=\frac{7}{4}\left(\frac{33}{12}+\frac{33}{20}+\frac{33}{30}+\frac{33}{42}\right)\)
\(=\frac{7}{4}.33\left(\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)\)
\(=\frac{231}{4}\left(\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\)
\(=\frac{231}{4}\left(\frac{1}{3}-\frac{1}{7}\right)\)
\(=\frac{231}{4}\cdot\frac{4}{21}=11\)
\(\left[\left(\frac{2}{193}-\frac{3}{386}\right).\frac{193}{17}+\frac{33}{34}\right]:\left[\left(\frac{7}{1931}+\frac{11}{3862}\right).\frac{1931}{25}+\frac{9}{2}\right]\)
= \(\left[\frac{193}{17}.\frac{2}{193}-\frac{193}{17}.\frac{3}{386}+\frac{33}{34}\right]:\left[\frac{1931}{25}.\frac{7}{1931}+\frac{1931}{25}.\frac{11}{3862}+\frac{9}{2}\right]\)
= \(\left[\frac{2}{17}-\frac{3}{17}+\frac{33}{34}\right]:\left[\frac{7}{25}+\frac{11}{50}+\frac{9}{2}\right]\)
= \(\left[\frac{4}{34}-\frac{6}{34}+\frac{33}{34}\right]:\left[\frac{14}{50}+\frac{11}{50}+\frac{225}{50}\right]\)
= \(\frac{31}{34}:2\)
= \(\frac{31}{68}\)
\(=\frac{16}{5}.\frac{15}{16}-\left(\frac{3}{4}+\frac{2}{7}\right):\left(\frac{-29}{28}\right)\)
\(=3-\left(\frac{21}{28}+\frac{8}{28}\right):\left(\frac{-29}{28}\right)\)
\(=3-\left(\frac{29}{28}\right).\left(\frac{-28}{29}\right)\)
\(=3-\left(-1\right)\)
\(=4\)
b) \(=\left(\frac{1}{4}+\frac{25}{2}-\frac{5}{16}\right):\left(12-\frac{7}{12}:\left(\frac{3}{8}-\frac{1}{12}\right)\right)\)
\(=\left(\frac{4}{16}+\frac{200}{16}-\frac{5}{16}\right):\left(12-\frac{7}{12}:\left(\frac{3.3}{2.3.4}-\frac{2}{2.3.4}\right)\right)\)
\(=\left(\frac{199}{16}\right):\left(12-\frac{7}{12}:\left(\frac{9}{24}-\frac{2}{24}\right)\right)\)
\(=\frac{199}{16}:\left(12-\frac{7}{12}.\frac{24}{7}\right)\)
\(=\frac{199}{16}:\left(12-2\right)\)
\(=\frac{199}{16}:10\)
\(=\frac{199}{160}\)
c) \(\left(\frac{-3}{5}+\frac{5}{11}\right):\frac{-3}{7}+\left(\frac{-2}{5}+\frac{6}{5}\right):\frac{-3}{7}\)
\(\left(\frac{-33}{55}+\frac{25}{55}\right):\frac{-3}{7}+\left(\frac{4}{5}\right):\frac{-3}{7}\)
\(\left(\frac{-8}{55}\right).\frac{-7}{3}+\frac{4}{5}.\frac{-7}{3}\)
\(\frac{-7}{3}\left(\frac{-8}{55}+\frac{4}{5}\right)\)
\(\frac{-7}{3}.\frac{36}{55}=\frac{-84}{55}\)
A = \(\frac{1}{2}-\frac{3}{4}+\frac{5}{6}-\frac{7}{12}\)
A = \(\left(-\frac{1}{4}\right)+\frac{5}{6}-\frac{7}{12}\)
A = \(\frac{7}{12}-\frac{7}{12}\)
A = \(0\).
Mình làm câu A thôi nhé.
Chúc bạn học tốt!
\(\left(5-\frac{43}{10}\right)-\left(\frac{42}{19}-\left(\frac{7}{2}-\frac{59}{10}\right)\right)+\frac{42}{19}+\frac{59}{10}+\frac{4}{5}\)
\(=5-\frac{43}{10}-\left(\frac{42}{19}-\frac{7}{2}+\frac{59}{10}\right)+\frac{42}{19}+\frac{59}{10}+\frac{4}{5}\)
\(=5-\frac{43}{10}-\frac{42}{19}+\frac{7}{2}-\frac{59}{10}+\frac{42}{19}+\frac{59}{10}+\frac{4}{5}\)
\(=5-\frac{43}{10}+\frac{7}{2}+\frac{4}{5}\)
\(=5+\frac{35}{10}+\frac{8}{10}-\frac{43}{10}=5\)
2)lx^2+lx+1ll=x^2
=>x^2+lx+1l=x^2=>lx+1l=0=>x=-1
3)\(\frac{\left(-\frac{1}{2}\right)^n}{\left(-\frac{1}{2}\right)^{n-2}}=\left(-\frac{1}{2}\right)^{n-n-2}=\left(-\frac{1}{2}\right)^{-2}=4\)
1)\(A=\frac{1}{41}+\frac{1}{42}+\frac{1}{43}+...+\frac{1}{80}\)
\(\Rightarrow A=\left(\frac{1}{41}+\frac{1}{42}+\frac{1}{43}+...+\frac{1}{60}\right)+\left(\frac{1}{61}+\frac{1}{62}+\frac{1}{63}+...+\frac{1}{80}\right)\)
\(\Rightarrow A=C+D\)
Ta có:\(\frac{1}{41}>\frac{1}{60};>\frac{1}{60}:\frac{1}{43}>\frac{1}{60};...;\frac{1}{59}>\frac{1}{60};\frac{1}{60}=\frac{1}{60}\)
\(\Rightarrow C=\frac{1}{41}+\frac{1}{42}+\frac{1}{43}+...+\frac{1}{60}>\frac{1}{60}+\frac{1}{60}+\frac{1}{60}+...+\frac{1}{60}\)
Ta thấy C có 20 số hạng
\(\Rightarrow C>\frac{1}{60}.20=\frac{1}{3}\)
Ta có:\(\frac{1}{61}>\frac{1}{80};\frac{1}{62}>\frac{1}{80};\frac{1}{63}>\frac{1}{80};...;\frac{1}{79}>\frac{1}{80};\frac{1}{80}=\frac{1}{80}\)
\(\Rightarrow D=\frac{1}{61}+\frac{1}{62}+\frac{1}{63}+...+\frac{1}{80}>\frac{1}{80}+\frac{1}{80}+\frac{1}{80}+...+\frac{1}{80}\)
Ta thấy D có 20 số hạng.
\(\Rightarrow D>\frac{1}{80}.20=\frac{1}{4}\)
\(\Rightarrow A=C+D>\frac{1}{3}+\frac{1}{4}=\frac{7}{12}\)
\(\Rightarrow A>B\)
Chọn phương án chính xác cho phép tính sau: \(-\frac{9}{12}-\left(\frac{-35}{42}\right)\) = ?
A. \(\frac{-9}{12}-\left(\frac{-35}{42}\right)=\frac{-9}{12_{\left(42\right)}}+\frac{35}{42_{\left(12\right)}}=\frac{-378+420}{504}=\frac{42}{504}=\frac{1}{12}\)
B. \(\frac{-9}{12}-\left(\frac{-35}{42}\right)=-\frac{9}{12}+\frac{35}{42}=-\frac{9}{12_{\left(7\right)}}+\frac{5}{7_{\left(12\right)}}=\frac{-63+60}{84}=-\frac{3}{84}=\frac{-1}{12}\)
so sánh hợp lí :
34/43 và 35/42