Saturday, 8 March 2014

Show, with induction that 12+22+....+n2=fracn(n+1)(2n+1)6

Show, with induction that



12+22+....+n2=n(n+1)(2n+1)6



My attempt



Case 1: n = 1



LHS=12




RHS=(1+1)(2+1)6=236=1



Case 2: n = p



LHSp=12+22+...+p2



RHSp=p(p+1)(2p+1)6



Case 3: n = p + 1




LHSp+1=12+22+....+p2+(p+1)2



RHSp+1=(p+1)((p+1)+1)(2(p+1)+1)6



Now to show this with induction I think i need to show that



RHSp+1=RHSp+(p+1)2



RHSp+1=p(p+1)(2p+1)6+(p+1)2




So I need to rewrite



RHSp+1=(p+1)((p+1)+1)(2(p+1)+1)6to be equal to p(p+1)(2p+1)6+(p+1)2
Anyone see how I can do that? Or got any other solution?

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