原式=[(2*2-1)/(2*2)]*[(3*3-1)/(3*3)]*……*[(2005*2005-1)/(2005*2005)]
=[(2+1)(2-1)/(2*2)]*[(3+1)(3-1)/(3*3)]*……*[(2005+1)(2005-1)/(2005*2005)]
=(1*2*3*3*4*4*……*2004*2004*2005*2006)/2*2*3*3*4*4*……*2005*2005
=1*2006/2*2005
=1003/2005
原式=[(2*2-1)/(2*2)]*[(3*3-1)/(3*3)]*……*[(2005*2005-1)/(2005*2005)]
=[(2+1)(2-1)/(2*2)]*[(3+1)(3-1)/(3*3)]*……*[(2005+1)(2005-1)/(2005*2005)]
=(1*2*3*3*4*4*……*2004*2004*2005*2006)/2*2*3*3*4*4*……*2005*2005
=1*2006/2*2005
=1003/2005