ummm

For question 1, some of my working out is:

(x+1)^3 - x^3 = 3x^2 + 3x + 1

x = 1 2^3 - 1^3 = 3 * 1^2 + 3 * 1 + 1

x = 2 3^3 - 2^3 = 3* 2^2 + 3 * 2 + 1

x = n (n+1)^3 - n^3 = 3 * n^3 - n^3 = 3 * n^2 + 3 * n + 1

(n + 1 - 1)((n+1)^2 + (n+1) + 1^2) = 3En^3 + (3*n(n+1))/2 + n

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Idno ...somehow we're meant to get En^2 = n/6(n+1)(2n+1) but I don't really noe the rite method to get to it