proof question

[ember osprey]

I got to this step but unsure on what to do

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[dim tree]

you’ve expanded many of the numbers wrong
you’ve done everything correct until (2n+1)(4n^2+ 4n+1) - (2n+1)

which gives you
8n^3 + 12n^2 +4n
and you would factorise
4(2n^3 + 3n^2 + n) which is a multiple of 4

b) if we let n=2 for example
(2)^3 - 2 = 6 which isn’t a multiple of 4