... minh cdng thUc vdi n = k + 1 k + k + '" 2k + \ 13 2{ k + \) 24 Bang cac phan tfch : 15 1 -; + + k +2 k+3 ^ 1 2k ' 2k + l 2ik + l) = + ^+1 k +2 2A: + 1 + + — 2k 2( it + l) k+l HS tur chiing minh tiep ... hdi Hay thidi lap va chiing minh Ta se chiing minh cdng thUc vdi n = k + 2^ + A^ + + {2kf + {2k + 2f, 2{ k+\)(k + 2) {2k + 2, ) Bang phuong pha'p quy nap HS tu chiing minh Bai Ihcdng ddn Sir dung ... 2, hay Ifnh luong long Irong n nam ,„ « [2. 36 + (/I - 1).3] • ; ^ ' - ,,::.::• 3n{n + 23 ) Gdi y tra ldi cau hdi „ 4« [2. 7 + (4/7 - 1) (),5| = 2/ 7 (2/ 7 + 13,5) Ggi y tra ldi cau hdi Cau hdi Ti T2-^i3-n)...