How far have you got with this question - what part are you looking for help with?
Take 3 consecutive numbers, e.g. 5,6,7.
- Square each one.
- Add the 3 squares.
- Subtract 2 from the sum.
- Divide the result by 3.
- Write down number.
- Take 3 other consecutive numbers 10, 11, 12 & repeat.
- Predict answer for 19, 20, 21.
- Using n, n+1, n+2 simplify and show how this pattern works.