急,我有d關於A Maths o既問題想問吓大家 (MI)

For n = k+1.
1/2*5 + 1/5*8 + ......+ 1/[3(k+1) - 1][3(k+1) + 2]
= k/(6k +4) + 1/(3k+2)(3k+ 5)
= [k(3k+5) + 2]/2(3k+2)(3k+5)
= [3k^2 + 5k +2]/2(3k+2)(3k+5)
= (3k + 2)(k + 1)/2(3k+2)(3k+5)
= (k+1)/2(3k+5)
= (k+1)/(6k + 10)
= (k+1)/[6(k+1) + 4].