Question

[Nguyen Huong Giang]

a) Tìm x :

 x - 2/11.13 - 2/13.15 - 2/15.17 - ... - 2/55.57= 4/3

b) Chứng tỏ rằng : 1/ 2^2 + 1/3^2 + 1/4^2 + ... + 1/100^2 <1

Answer 1

[✓ ℍɠŞ_ŦƦùM $₦G ✓]

a.x-2/11.13-2/13.15-2/15.17-...-2/55.57=4/3

=>x-(2/11.13+2/13.15+2/15.17+...+2/55.57)=4/3

=>x-(1/11-1/13+1/13-1/15+...+1/55-1/57)=4/3

=>x-(1/11-1/57)=4/3

=>x-46/627=4/3

=>x=4/3+46/627=294/209