\(\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}+\frac{2}{11.13}+\frac{2}{13.15}\)
\(=\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}+...+\frac{1}{13}-\frac{1}{15}\)
\(=\frac{1}{5}-\frac{1}{15}=\frac{3}{15}-\frac{1}{15}=\frac{3-1}{15}=\frac{2}{15}\)
P/s : Dấu chấm là nhân nhé!
2/5x7+2/7x9+2/9x11+...+2/13x15
=1/5x7+1/7x9+1/9x11+...+1/13x15
=1/5-1/15
=3/15-1/15
=2/15
\(\frac{2}{5x7}\)+\(\frac{2}{7x9}\)+\(\frac{2}{9x11}\)+\(\frac{2}{11x13}\)+\(\frac{2}{13x15}\)=
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 !!!
\(\frac{2}{5x7}\)+ \(\frac{2}{7x9}\)+ \(\frac{2}{9x11}\)+ \(\frac{2}{11x13}\)+ \(\frac{2}{13x15}\)
Tìm y biết:
\(\left(\frac{2}{1x3}+\frac{2}{3x5}+\frac{2}{5x7}+\frac{2}{7x9}+\frac{2}{9x11}\right)\cdot y=\frac{2}{3}\)
Tính Nhanh
a) \(\frac{1995x1997-1}{1996x1995+199}\) b) \(\frac{2}{3x5}\) + \(\frac{2}{5x7}\) + \(\frac{2}{7x9}\) + \(\frac{2}{9x11}\) + ..... + \(\frac{2}{13x15}\)
\(\left(\frac{1}{1x3}+\frac{1}{3x5}+\frac{1}{5x7}+\frac{1}{7x9}+\frac{1}{9x11}\right)\)
Tính
\(\frac{1}{1x3}+\frac{1}{3x5}+\frac{1}{5x7}+\frac{1}{7x9}+\frac{1}{9x11}\)
1, Tìm x
\(\frac{1}{5x7}+\frac{1}{7x9}+\frac{1}{9x11}+.....+\frac{1}{2009x2011}+\frac{1}{x}=\frac{1}{5}x0,5\)
Tính nhanh tổng sau:
\(\frac{2}{1x3}\)+ \(\frac{2}{3x5}\)+ \(\frac{2}{5x7}\)+ \(\frac{2}{7x9}\)+ \(\frac{2}{9x11}\)+ \(\frac{2}{11x13}\)
Ai lam dung va nhanh nhat, minh tick cho!
