1/(2n-1)(2n+1)=1/2[1/(2n-1)-1/(2n+1)]
Sn=1/2[1/1-1/3+1/3-1/5+1/5-1/7.+1/(2n-1)-1/(2n-1)]
=1/2[1-1/(2n-1)]
=1/2[(2n-2)/(2n-1)]
=(n-1)/(2n-1)
limSn=lim(n-1)/(2n-1)=lim(1-1/n)/(2-1/n)=1/2
不一定都要先求Sn
但先求对解极限方便...
1/(2n-1)(2n+1)=1/2[1/(2n-1)-1/(2n+1)]
Sn=1/2[1/1-1/3+1/3-1/5+1/5-1/7.+1/(2n-1)-1/(2n-1)]
=1/2[1-1/(2n-1)]
=1/2[(2n-2)/(2n-1)]
=(n-1)/(2n-1)
limSn=lim(n-1)/(2n-1)=lim(1-1/n)/(2-1/n)=1/2
不一定都要先求Sn
但先求对解极限方便...