Q:

Use induction to prove the following formula is true for all integers n where n greaterthanorequalto 1. 1 + 4 + 9 + .. + n^2 = n(n + 1)(2n + 1)/6

Accepted Solution

A:
Answer with Step-by-step explanation:Since we have given that 1+4+9+........................+n² = [tex]\dfrac{n(n+1)(2n+1)}{6}[/tex]We will show it using induction on n:Let n = 1L.H.S. :1 = R.H.S. : [tex]\dfrac{1\times 2\times 3}{6}=\dfrac{6}{6}=1[/tex]So, P(n) is true for n = 1Now, we suppose that P(n) is true for n = k.[tex]1+4+9+...................+k^2=\dfrac{k(k+1)(2k+1)}{6}[/tex]Now, we will show that P(n) is true for n = k+1.So, it L.H.S. becomes,[tex]1+4+9+......................+(k+1)^2[/tex]and R.H.S. becomes,[tex]\dfrac{(k+1)(k+2)(2k+3)}{6}[/tex]Consider, L.H.S.,[tex]1+4+9+..+k^2+(k+1)^2\\\\=\dfrac{k(k+1)(2k+1)}{6}+(k+1)^2\\\\=k+1[\dfrac{k(2k+1)}{6}+(k+1)]\\\\=(k+1)[\dfrac{2k^2+k+6k+6}{6}]\\\\=(k+1)\dfrac{2k^2+7k+6}{6}]\\\\=(k+1)\dfrac{2k^2+4k+3k+6}{6}]\\\\=(k+1)[\dfrac{2k(k+2)+3(k+2)}{6}]\\\\=\dfrac{(k+1)(2k+3)(k+2)}{6}[/tex]So, L.H.S. = R.H.S.Hence, P(n) is true for all integers n.