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YM
3
3 tháng 7 2018
\(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+....+\frac{2}{575}+\frac{2}{675}\)
\(=\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+...+\frac{2}{23\times25}+\frac{2}{25\times27}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{23}-\frac{1}{25}+\frac{1}{25}-\frac{1}{27}\)
\(=\frac{1}{3}-\frac{1}{27}=\frac{8}{27}\)
Vậy ....
3 tháng 7 2018
\(\frac{2}{15}+\frac{2}{35}+\frac{2}{69}+........+\frac{2}{575}+\frac{2}{675}\)
\(=\frac{2}{3\times5}+\frac{2}{5\times7}+........+\frac{2}{23\times25}+\frac{2}{25\times27}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+.......+\frac{1}{23}-\frac{1}{25}+\frac{1}{25}-\frac{1}{27}\)
\(=\frac{1}{3}-\frac{1}{27}\)
\(=\frac{8}{27}\)
KC
6
WH
19 tháng 5 2018
\(17,8-\left(14,904:3\cdot y-1,084\right)-2,63=13,77\)
\(\Leftrightarrow4,968\cdot y-1,084=17,8-\left(13,77+2,63\right)\)
\(\Leftrightarrow4,968\cdot y-1,084=17,8-16,4\)
\(\Leftrightarrow4,968\cdot y=17,8-16,4+1,084\)
\(\Leftrightarrow4,968\cdot y=2,484\)
\(\Leftrightarrow y=2,484:4,968\)
\(\Leftrightarrow y=0,5\)
19 tháng 5 2018
\(17,8-\left(14,904:3.y-1,084\right)-2,63=13,77\)
\(\Leftrightarrow17,8-\left(4,968.y-1,084\right)=13,77+2,63\)
\(\Leftrightarrow17,8-\left(4,968.y-1,084\right)=16,4\)
\(\Leftrightarrow4,968.y-1,084=17,8-16,4\)
\(\Leftrightarrow4,968.y-1,084=1,4\)
\(\Leftrightarrow4,968.y=1,4+1,084\)
\(\Leftrightarrow4,968.y=2,484\)
\(\Leftrightarrow y=2,484:4,968\)
\(\Leftrightarrow y=0,5\)
Vậy y = 0,5
_Chúc bạn học tốt_
NH
30 tháng 3 2019
\((\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99})x=\frac{2}{3}\)
Đặt \(A=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\)
\(A=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\)
\(A=\frac{1}{2}\left(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{9.11}\right)\)
\(A=\frac{1}{2}\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{11}\right)\)
\(A=\frac{1}{2}\left(1-\frac{1}{11}\right)\)
\(A=\frac{1}{2}.\frac{10}{11}=\frac{5}{11}\)
Thay A vào biểu thức
\(\Rightarrow\frac{5}{11}x=\frac{2}{3}\)
\(\Rightarrow x=\frac{22}{15}\)
P/s: Có thể tính sai :(
30 tháng 3 2019
\(\left[\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right]\times x=\frac{2}{3}\)
Trước tiên mình tính dãy có dấu ngoặc đã
Đặt : \(S=\frac{1}{3}+\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\)
\(=\frac{1}{2}\left[\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+\frac{1}{7\cdot9}+\frac{1}{9\cdot11}\right]\)
\(=\frac{1}{2}\left[\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+\frac{2}{9\cdot11}\right]\)
\(=\frac{1}{2}\left[1-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{11}\right]\)
\(=\frac{1}{2}\left[1-\frac{1}{11}\right]=\frac{1}{2}\cdot\frac{10}{11}=\frac{1\cdot10}{2\cdot11}=\frac{1\cdot5}{1\cdot11}=\frac{5}{11}\)
Thay vào biểu thức \(S=\frac{5}{11}\)ta lại có :
\(\frac{5}{11}\times x=\frac{2}{3}\)
\(\Leftrightarrow x=\frac{2}{3}:\frac{5}{11}\)
\(\Leftrightarrow x=\frac{2}{3}\cdot\frac{11}{5}\)
\(\Leftrightarrow x=\frac{22}{15}\)
Vậy \(x=\frac{22}{15}\)
T
2 tháng 7 2019
#)Giải :
\(200-18:\left(372:3x-1\right)-28=166\)
\(\Leftrightarrow200-18:\left(372:3x-1\right)=194\)
\(\Leftrightarrow18:\left(372:3x-1\right)=6\)
\(\Leftrightarrow372:3x-1=3\)
\(\Leftrightarrow3x-1=124\)
\(\Leftrightarrow3x=125\)
\(\Leftrightarrow x=\frac{125}{3}\)
XO
2 tháng 7 2019
200 - 18 : (372 : 3 . x - 1) - 28 = 166
=> 200 - 18 : (372 : 3.x - 1) = 166 + 28
=> 200 - 18 : (372 : 3.x) - 1) = 194
=> 18 : (372 : 3.x - 1) = 200 - 194
=> 18 : (372 : 3.x - 1) = 6
=> 372 : 3.x - 1 = 18 : 6
=> 372 : 3.x - 1 = 3
=> 372 : 3.x = 3 + 1
=> 372 : 3.x = 4
=> 3.x = 372 : 4
=> 3.x = 93
=> x = 93 : 3
=> x = 31
26 tháng 8 2020
\(\left(\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)×x=\frac{6}{5}\)
\(\frac{3}{55}×x=\frac{6}{5}\)
\(x=\frac{6}{5}:\frac{3}{55}\)
\(x=22\)
vậy \(x=22\)
VM
26 tháng 8 2020
\(\left(\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right).x=\frac{6}{5}\)
\(\Leftrightarrow\left(\frac{1.99}{35.99}+\frac{1.55}{63.55}+\frac{1.35}{99.35}\right).x=\frac{6}{5}\)
\(\Leftrightarrow\left(\frac{99}{3465}+\frac{55}{3465}+\frac{35}{3465}\right).x=\frac{6}{5}\)
\(\Leftrightarrow\left(\frac{99+55+35}{3465}\right).x=\frac{6}{5}\)
\(\Leftrightarrow\frac{189}{3465}.x=\frac{6}{5}\)
\(\Leftrightarrow\frac{3}{55}.x=\frac{6}{5}\)
\(\Leftrightarrow x=\frac{6}{5}:\frac{3}{55}\)
\(\Leftrightarrow x=\frac{6}{5}.\frac{55}{3}\)
\(\Leftrightarrow x=\frac{330}{15}\)
\(\Leftrightarrow x=22\)
Vậy \(x=22.\)
XO
29 tháng 7 2019
\(\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\times x=1\)
\(\Rightarrow\left(\frac{1}{3\times5}+\frac{1}{5\times7}+\frac{1}{7\times9}+\frac{1}{9\times11}\right)\times x=1\)
\(\Rightarrow\frac{1}{2}\times\left(\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}+\frac{2}{9\times11}\right)\times x=1\)
\(\Rightarrow\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\times x=1\)
\(\Rightarrow\frac{1}{2}\times\left(\frac{1}{3}-\frac{1}{11}\right)\times x=1\)
\(\Rightarrow\frac{1}{2}\times\frac{8}{33}\times x=1\)
\(\Rightarrow\frac{4}{33}\times x=1\)
\(\Rightarrow x=1:\frac{4}{33}\)
\(\Rightarrow x=\frac{33}{4}\)
Vậy \(x=\frac{33}{4}\)
2,63 x 99 + 2,63
= 2,63 x 99 + 2,63 x 1
= 2,63 x ( 99 + 1 )
= 2,63 x 100
= 263
Học tốt ! ^^
2,63 x 99 + 2,63
= 2,63 x (99 + 1)
= 2,63 x 100
= 263