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\(\frac{1}{1}\cdot\frac{1}{2}+\frac{1}{2}\cdot\frac{1}{3}+\frac{1}{3}\cdot\frac{1}{4}+\frac{1}{4}\cdot\frac{1}{5}+\frac{1}{5}\cdot\frac{1}{6}=\)
\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}=\)
\(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}=\)
\(\frac{1}{1}-\frac{1}{6}=\frac{5}{6}\)
k nha gõ mỏi tay lắm
Bài 2
a) \(x\times1\frac{1}{4}=3\frac{3}{4}\)
\(x\times\frac{5}{4}=\frac{15}{4}\)
\(x=\frac{15}{4}.\frac{4}{5}\)
\(x=3\)
b) \(x-\frac{3}{4}=6\times\frac{3}{8}\)
\(x-\frac{3}{4}=\frac{9}{4}\)
\(x=\frac{9}{4}+\frac{3}{4}\)
\(x=3\)
Những câu còn lại tương tự
a)\(\left(x+3\right)\times5+1=20\Leftrightarrow5x+15=19\)
\(\Leftrightarrow5x=4\Leftrightarrow x=\frac{4}{5}\)
b)sai đề
c)\(2\frac{3}{7}\times x+1\frac{5}{4}=5\frac{3}{42}\)\(\Leftrightarrow\frac{17}{7}\times x+\frac{9}{4}=\frac{71}{14}\) \(\Leftrightarrow\frac{17}{7}\times x+\frac{63}{28}=\frac{142}{28}\)
\(\Leftrightarrow\frac{17}{7}\times x=\frac{79}{28}\Leftrightarrow x=\frac{17}{7}:\frac{79}{28}\) \(\Leftrightarrow x=\frac{17}{7}\times\frac{28}{79}\Leftrightarrow x=\frac{476}{553}=\frac{68}{79}\)
d)\(10\frac{2}{3}-x:\frac{6}{7}=8\frac{1}{3}-6\frac{2}{7}\Leftrightarrow\frac{32}{3}-x:\frac{6}{7}=\frac{25}{3}-\frac{44}{7}\) \(\Leftrightarrow\frac{224}{21}-x:\frac{6}{7}=\frac{75}{21}-\frac{132}{21}\Leftrightarrow-\frac{57}{21}-\frac{224}{21}\)
\(\Leftrightarrow-x:\frac{6}{7}=-\frac{281}{21}\Leftrightarrow-x=-\frac{281}{21}\times\frac{6}{7}\) \(\Leftrightarrow-x=-\frac{1686}{147}\Leftrightarrow x=\frac{562}{49}=11\frac{23}{49}\)
a, x + 2/5 = 1/2
x = 1/2 + 2/5
x = 9/10 b,34/5 + x = 15/8
x = 34/5 - 15/8
x =197/40 c, x - 45/6 = 21/6 + 5/6
x - 45/6 = 26/6
x = 26/6 + 45/6
x =71/6 d,14/5 - x = 11/5 - 3/5
14/5 - x = 8/5
x = 14,5 - 8/5
x =6/5
a, x + 2/5 = 1/2
x = 1/2 + 2/5
x = 9/10
b,34/5 + x = 15/8
x = 34/5 - 15/8
x =197/40
c, x - 45/6 = 21/6 + 5/6
x - 45/6 = 26/6
x = 26/6 + 45/6
x =71/6
d,14/5 - x = 11/5 - 3/5
14/5 - x = 8/5
x = 14,5 - 8/5
x =6/5
- Làm lại.
C= \(\frac{1}{1x3x5}+\frac{1}{3x5x7}+....+\frac{1}{101x103x105}\)
4C=\(\frac{4}{1x3x5}+\frac{4}{3x5x7}+\frac{4}{5x7x9}+....+\frac{4}{101x103x105}\)
4C=\(\frac{5-1}{1x3x5}+\frac{7-3}{3x5x7}+...+\frac{105-101}{101x103x105}\)
4C=\(\frac{1}{1x3}-\frac{1}{3x5}+\frac{1}{3x5}-\frac{1}{5x7}+.....+\frac{1}{101x103}-\frac{1}{103x105}\)
4C=\(\frac{1}{1x3}-\frac{1}{103x105}\)
4C=..........
C=..........
tự làm nốt nha bạn và nhớ k nha
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