# Two induction exercise

• Oct 11th 2011, 11:47 AM
Kelvin88
Two induction exercise
Hi!

Can anyone help me solcing these excercises please?

a. Prove that 1*2+2*3+...+n(n+1)=[n(n+1)(n+2)]/3

b. 1*2*3+2*3*4+...+n(n+1)(n+2)=?

Cheers
• Oct 11th 2011, 11:55 AM
Plato
Re: Two induction exercise
Quote:

Originally Posted by Kelvin88
Can anyone help me solcing these excercises please?
a. Prove that 1*2+2*3+...+n(n+1)=[n(n+1)(n+2)]/3
b. 1*2*3+2*3*4+...+n(n+1)(n+2)=?

What have you tried?
• Oct 11th 2011, 11:58 AM
emakarov
Re: Two induction exercise
There is a plan to follow for each proof by induction, and you don't have to think much to advance quite a bit. If you don't have anything better, you can find one description here. Or explain what exactly you don't understand. See also rule #11 in this sticky thread.
• Oct 11th 2011, 12:12 PM
Kelvin88
Re: Two induction exercise
Ok, i understand. I am sorry, actually these are from my homework (the easier ones), but have no idea how to start. Maybe at a. I should prove for P(1), then for P(n+1)? Then it will be 1*2+2*3+...+(n+1)(n+2) ?
For b. I have no idea what should I do:(
• Oct 11th 2011, 12:27 PM
emakarov
Re: Two induction exercise
Quote:

Originally Posted by Kelvin88
Maybe at a. I should prove for P(1), then for P(n+1)? Then it will be 1*2+2*3+...+(n+1)(n+2) ?