Đáp án: GỌi A=1-1/2^2-1/3^2-1/4^2-...-1/2011^2
Ta có:
vì 1/1.2>1/2^2
1/2.3>1/3^2
........................................
1/2010.2011>1/2011^2
=>A=1-1/2^2-1/3^2-1/4^2-...-1/2011^2>1-1/1.2-1/2.3-1/3.4-.................-1/2010.2011
=1-(1-1/2)-(1/2-1/3)-.......................-(1/2010-1/2011)
=1-1+1/2-1/2+1/3-1/3+................+1/2010-1/2010+1/2011
=(1-1)+(1/2-1/2)+(1/3-1/3)-................+(1/2010-1/2010)+1/2011
=0+0+......+0+1/2011=1/2011
=>A>1/2011
Vậy A>1/2011
Cho mình xin câu trả lời hay nhất nha
Thank you very much
