Question

[Lê Vũ Thu Hà]

tính nhanh các tổng sau : I : ( 1 - \(\frac{1}{2}\)) x ( 1- \(\frac{1}{3}\)) x ( 1 - \(\frac{1}{4}\)) x ......x ( 1 - \(\frac{1}{2006}\)) x ( 1 - \(\frac{1}{2007}\)) 

Answer 1

[# APTX _ 4869 _ : ( $>$ )]

(1-1/2)×(1-1/3)×(1-1/4 )×...×(1-1/2006)×(1-1/2007)

=(2/2-1/2)×(3/3-1/3)×(4/4-1/4)×..×(2006/2006-1/2006)×(2007/2007-1/2007)

=1/2×2/3×3/4×..×2005/2006×2006/2007

=1/2007