3.(1/4.5+1/5.6+...+1/9.10).x=9/2
3.(1/4-1/5+1/5-1/6+...+1/9-1/10).x=9/2
3.(1/4-1/10).x=9/2
3.3/20.x=9/2
9/20.x=9/2
x=9/2:9/20
x=10
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Chương I : Ôn tập và bổ túc về số tự nhiên
Các câu hỏi tương tự
Bài 1: Tìm số hữu tỉ x và y biết:
dfrac{x}{6} - dfrac{1}{y} dfrac{1}{2}
Bài 2: Tính nhanh
dfrac{7}{3.4} - dfrac{9}{1.5} + dfrac{11}{5.6} - dfrac{13}{6.7} + dfrac{15}{7.8} - dfrac{17}{8.9} + dfrac{19}{9.10}
(Mấy cái dấu chấm đấy là dấu nhân nhé!!!)
Đọc tiếp
Bài 1: Tìm số hữu tỉ x và y biết:
\(\dfrac{x}{6}\) - \(\dfrac{1}{y}\) = \(\dfrac{1}{2}\)
Bài 2: Tính nhanh
\(\dfrac{7}{3.4}\) - \(\dfrac{9}{1.5}\) + \(\dfrac{11}{5.6}\) - \(\dfrac{13}{6.7}\) + \(\dfrac{15}{7.8}\) - \(\dfrac{17}{8.9}\) + \(\dfrac{19}{9.10}\)
(Mấy cái dấu chấm đấy là dấu nhân nhé!!!)
1) Tìm x biết:
\(\left(1-\dfrac{3}{10}-x\right):\left(\dfrac{19}{10}-1-\dfrac{2}{5}\right)+\dfrac{4}{5}=1\)
2) Tính nhanh
a)\(\dfrac{1}{1.2.3}+\dfrac{1}{2.3.4}+\dfrac{1}{3.4.5}+...+\dfrac{1}{10.11.12}\)
b)\(\dfrac{1^2}{1.2}.\dfrac{2^2}{2.3}.\dfrac{3^2}{3.4}.\dfrac{4^2}{4.5}\)
3 tìm x biết
\(\dfrac{111}{37}< x< \dfrac{91}{13}x\)e Z
b) \(\dfrac{-84}{14}< x< \dfrac{108}{9}\)
4 Tìm x
a ) \(\dfrac{x-1}{9}=\dfrac{8}{3}\)
b) \(\dfrac{-x}{4}=\dfrac{-9}{x}\)
c ) \(\dfrac{x}{4}=\dfrac{18}{x+1}\)
Bài 17 Tìm x biết :
a) \(\dfrac{x}{5}=\dfrac{2}{5}\)
b) \(\dfrac{3}{8}=\dfrac{6}{x}\)
c) \(\dfrac{1}{9}=\dfrac{x}{27}\)
d) \(\dfrac{4}{x}=\dfrac{8}{6}\)
e) \(\dfrac{3}{x-5}=\dfrac{-4}{x+2}\)
g) \(\dfrac{x}{-2}=\dfrac{-8}{x}\)
Bài 1:
a,|x-3|+|2-x|0
b,left(2-dfrac{3}{4}xright).left(x+1right)0
bài 2:
a,Adfrac{dfrac{-6}{7}+dfrac{6}{13}-dfrac{6}{29}}{dfrac{9}{7}-dfrac{9}{13}+dfrac{9}{29}}
b,Bdfrac{dfrac{2}{15}-dfrac{2}{21}+dfrac{2}{39}}{0,25-dfrac{5}{28}+dfrac{5}{52}}
c,Cdfrac{50-dfrac{4}{15}+dfrac{2}{15}-dfrac{2}{17}}{100-dfrac{8}{13}+dfrac{4}{15}-dfrac{4}{17}}:dfrac{1+dfrac{2}{21}-dfrac{5}{121}}{dfrac{65}{121}-dfrac{26}{71}-13}
Đọc tiếp
Bài 1:
a,\(|x-3|+|2-x|=0\)
b,\(\left(2-\dfrac{3}{4}x\right).\left(x+1\right)=0\)
bài 2:
a,A=\(\dfrac{\dfrac{-6}{7}+\dfrac{6}{13}-\dfrac{6}{29}}{\dfrac{9}{7}-\dfrac{9}{13}+\dfrac{9}{29}}\)
b,B=\(\dfrac{\dfrac{2}{15}-\dfrac{2}{21}+\dfrac{2}{39}}{0,25-\dfrac{5}{28}+\dfrac{5}{52}}\)
c,C=\(\dfrac{50-\dfrac{4}{15}+\dfrac{2}{15}-\dfrac{2}{17}}{100-\dfrac{8}{13}+\dfrac{4}{15}-\dfrac{4}{17}}:\dfrac{1+\dfrac{2}{21}-\dfrac{5}{121}}{\dfrac{65}{121}-\dfrac{26}{71}-13}\)
1.
a, ^{^2}left(x-2right)9 b,^{^3}left(3x-1right)-8 c, left(x+dfrac{1}{2}right)^2dfrac{1}{16} d, left(dfrac{2}{3}right)^xdfrac{4}{9} e, left(dfrac{1}{2}right)^{x-1}dfrac{1}{16} f,left(dfrac{1}{2}right)^{2x-1}8
2.tìm số tự nhiên n biết
a, 3^{n-1}27 b, 3^{n-1}dfrac{1}{243} c, left(dfrac{1}{2}right)^{2n-1}dfrac{1}{8} d, left(-dfrac{1}{3}right)^{n-5}dfrac{1}{81} e,2^{-1}.2^n+4.2^n9.2^5
Đọc tiếp
1.
a, \(^{^2}\left(x-2\right)=9\) b,\(^{^3}\left(3x-1\right)=-8\) c, \(\left(x+\dfrac{1}{2}\right)^2=\dfrac{1}{16}\) d, \(\left(\dfrac{2}{3}\right)^x=\dfrac{4}{9}\) e, \(\left(\dfrac{1}{2}\right)^{x-1}=\dfrac{1}{16}\) f,\(\left(\dfrac{1}{2}\right)^{2x-1}=8\)
2.tìm số tự nhiên n biết
a, \(3^{n-1}=27\) b, \(3^{n-1}=\dfrac{1}{243}\) c, \(\left(\dfrac{1}{2}\right)^{2n-1}=\dfrac{1}{8}\) d, \(\left(-\dfrac{1}{3}\right)^{n-5}=\dfrac{1}{81}\) e,\(2^{-1}.2^n+4.2^n=9.2^5\)
1 .Tìm x biết
a. ( dfrac{1}{1.4}+dfrac{1}{4.7}+dfrac{1}{7.10}+...+dfrac{1}{97.100}) dfrac{0,33x}{2009}
b. 1 + dfrac{1}{3}+dfrac{1}{6}+dfrac{1}{10}+...+dfrac{2}{xleft(x+1right)}1dfrac{1991}{1993}
c. dfrac{1}{2013}x+1+dfrac{1}{2}+dfrac{1}{6}+dfrac{1}{12}+...+dfrac{1}{2012.2013}2
d. 2x + dfrac{7}{6}+dfrac{13}{12}+dfrac{21}{20}+dfrac{31}{30}+dfrac{43}{42}+dfrac{57}{56}+dfrac{73}{72}+dfrac{91}{90}10
2. Chứng minh rằng :
a. dfrac{1}{4}+dfrac{1}{4^2}+dfrac{1}{4^3}+...+dfrac{1}{4^{99}} dfrac{1}{3...
Đọc tiếp
1 .Tìm x biết
a. ( \(\dfrac{1}{1.4}+\dfrac{1}{4.7}+\dfrac{1}{7.10}+...+\dfrac{1}{97.100}\)) = \(\dfrac{0,33x}{2009}\)
b. 1 + \(\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{10}+...+\dfrac{2}{x\left(x+1\right)}=1\dfrac{1991}{1993}\)
c. \(\dfrac{1}{2013}x+1+\dfrac{1}{2}+\dfrac{1}{6}+\dfrac{1}{12}+...+\dfrac{1}{2012.2013}=2\)
d. 2x + \(\dfrac{7}{6}+\dfrac{13}{12}+\dfrac{21}{20}+\dfrac{31}{30}+\dfrac{43}{42}+\dfrac{57}{56}+\dfrac{73}{72}+\dfrac{91}{90}=10\)
2. Chứng minh rằng :
a. \(\dfrac{1}{4}+\dfrac{1}{4^2}+\dfrac{1}{4^3}+...+\dfrac{1}{4^{99}}< \dfrac{1}{3}\)
b. \(\dfrac{1}{1.2.3}+\dfrac{1}{2.3.4}+...+\dfrac{1}{18.19.20}< \dfrac{1}{4}\)
Tìm tông x và y biết:
\(\dfrac{-3}{6}=\dfrac{x}{2}=\dfrac{-18}{y}\)
Giúp tui zí=)))
Tìm x biết
\(\dfrac{1}{3}+\dfrac{1}{6}+\dfrac{1}{10}+...+\dfrac{2}{x\left(x+1\right)}=\dfrac{2011}{2013}\)