Giúp mình vs ! tìm tổng của E nhé
\(E=\frac{2}{3x5}+\frac{2}{5x7}+.....+\frac{2}{17x19}\)
\(\frac{2}{3x5}+\frac{2}{5x7}+\frac{2}{7x9}+...+\frac{2}{17x19}\)
\(A=\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+...+\frac{2}{17\cdot19}\)
\(A=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{17}-\frac{1}{19}\)
\(A=\frac{1}{3}-\frac{1}{19}\)
\(A=\frac{16}{57}\)
Dấu "." là dấu nhân nhá ^^
\(\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{17\cdot19}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{17}-\frac{1}{19}\)
\(=\frac{1}{3}-\frac{1}{19}\)
\(=\frac{16}{57}\)
\(\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{17\times19}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{17}-\frac{1}{19}\)
\(=\frac{1}{3}-\frac{1}{19}\)
\(=\frac{16}{57}\)
Code : Breacker
Tìm X : (\(\frac{2}{3x5}\)+ \(\frac{2}{5x7}\)+ ... + \(\frac{2}{17x19}\)) x 57 - 2 x (X - 1) = 10
\(\left(\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{17\times19}\right)\times57-2\times\left(x-1\right)=10\)
\(\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{17}-\frac{1}{19}\right)\times57-2\times\left(x-1\right)=10\)
\(\left(\frac{1}{3}-\frac{1}{19}\right)\times57-2\times\left(x-1\right)=10\)
\(\frac{16}{57}\times57-2\times\left(x-1\right)=10\)
\(16-2\times\left(x-1\right)=10\)
\(2\times\left(x-1\right)=16-10\)
\(2\times\left(x-1\right)=6\)
\(x-1=6:2\)
\(x-1=3\)
\(x=3+1\)
\(x=4\)
Giúp với ạ
2/1x3 + 2/3x5 + 2/5x7 +...+2/15x17 + 2/17x19
Tính:
M = \(\frac{2}{3x5}\)+ \(\frac{2}{5x7}\)+ \(\frac{2}{7x9}\)+ ........ + \(\frac{2}{97x99}\)
Giúp mình với, x là nhân nhé
M=1/3-1/5+1/5-1/7+.....+1/97-1/99
M=1/3-1/199
M=32/99
\(M=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{97.99}\)
\(M=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{97}-\frac{1}{99}\)
\(M=\frac{1}{3}-\frac{1}{99}\)
\(M=\frac{32}{99}\)
~Học tốt~
\(M=\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{97.99}\)
\(=\)\(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{97}-\frac{1}{99}\)
\(=\)\(1-\frac{1}{99}\)
\(=\)\(\frac{98}{99}\)
vậy \(M=\frac{98}{99}\)
tính nhanh
\(\frac{2}{3x5}+\frac{2}{5x7}+\frac{2}{7x9}+\frac{2}{9x11}+\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{1x2}+\frac{2}{2x3}+\frac{2}{3x4}+...+\frac{2}{8x9}+\frac{2}{9x10}\)
giải hẳn ra cho mình ai làm đúng mình tk cho nhé !!!
\(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{13.15}+\frac{2}{1.2}+\frac{2}{2.3}+...+\frac{2}{9.10}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{13}-\frac{1}{15}+2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(=\frac{1}{3}-\frac{1}{15}+2\left(1-\frac{1}{10}\right)\)
\(=\frac{4}{15}+\frac{9}{5}\)
\(=\frac{31}{15}\)
Bài làm :
Ta có :
\(\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{13\times15}+\frac{2}{1\times2}+\frac{2}{2\times3}+...+\frac{2}{9\times10}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{13}-\frac{1}{15}+2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(=\frac{1}{3}-\frac{1}{15}+2\left(1-\frac{1}{10}\right)\)
\(=\frac{31}{15}\)
Tính nhanh
a) \(\frac{2}{1x3}+\frac{2}{3x5}+\frac{2}{5x7}+\frac{2}{7x9}\)
làm chi tiết hộ mình nhé nhưng nhớ là tính nhanh
\(\frac{2}{1\times3}+\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}\)
\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}\)
\(=1-\frac{1}{9}=\frac{8}{9}\)
\(\frac{2}{1\times3}+\frac{2}{3\times5}+\frac{2}{5\times7}+\frac{2}{7\times9}\)
\(=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}\)
\(=1+\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{1}{7}-\frac{1}{7}\right)-\frac{1}{9}\)
\(=1-\frac{1}{9}=\frac{8}{9}\)
~ Hok tốt ~
1/1x3+1/3x5+1/5x7+...+1/17x19 giúp mình nha
`1/[1xx3]+1/[3xx5]+1/[5xx7]+...+1/[17xx19]`
`=1/2xx(2/[1xx3]+2/[3xx5]+....+2/[17xx19])`
`=1/2xx(1-1/3+1/3-1/5+....+1/17-1/19)`
`=1/2xx(1-1/19)`
`=1/2xx18/19`
`=9/19`
2/3x5+2/5x7+...+2/17x19
\(\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{17.19}\)
= \(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{17}-\frac{1}{19}\)
= \(\frac{1}{3}-\frac{1}{19}\)
= \(\frac{16}{57}\)
\(\frac{2}{3.5}+\frac{2}{5.7}+.....+\frac{2}{17.19}\)
\(=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+.....+\frac{1}{17}-\frac{1}{19}\)
\(=\frac{1}{3}-\frac{1}{19}\)
\(=\frac{19}{57}-\frac{3}{57}\)
\(=\frac{16}{57}\)
vậy ......
chúc bạn học tốt!
tính nhanh C= \(\frac{2}{3x5}+\frac{2}{3x5}+\frac{2}{5x7}+...............+\frac{2}{2007x2009}\)
\(C=\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{2007\times2009}\)
\(C=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2007}-\frac{1}{2009}\)
\(C=\frac{1}{3}-\frac{1}{2009}=\frac{2006}{6027}\)
2/3x5=1/3-1/5
2/5x7=1/5-1/7.........
2/2005x2007=1/2005-1/2007
2/2007x2009=1/2007-1/2009
CỘNG THEO TÙNG VẾ TA ĐƯỢC
C=1/3-1/2009=2006/3X2009
2/3X5=1/3-1/5
2/5X7=1/5-1/7
..................
2/2005X2007=1/2005-1/2007
1/2007X2009=1/2007-1/2009
CỘNG THEO TÙNG VẾ TA ĐƯỢC C=1/3-1/2009=2006/3X2009