Question

tính nhanh C= \(\frac{2}{3x5}+\frac{2}{3x5}+\frac{2}{5x7}+...............+\frac{2}{2007x2009}\)

Answer 1

\(C=\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{2007\times2009}\)

\(C=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2007}-\frac{1}{2009}\)

\(C=\frac{1}{3}-\frac{1}{2009}=\frac{2006}{6027}\)

Answer 2

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

Answer 3

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

Answer 4

\(C=\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{2007.2009}\)

\(C=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+..+\frac{1}{2007}-\frac{1}{2009}\)

\(C=\frac{1}{3}-\frac{1}{2009}=\frac{2006}{6027}\)