Algebraic Proof help

[Wiltinglillies]

I am supposed to be helping with this. I can do (c), but totally stumped by questions (a) and (b). If I simplify the left side of (a) I just get 24, and for (b) I get -10.
Help!!!!

[dementedpixie]

You need to multiply it out properly:
(n+5)² - (n+1)²
= (n+5)(n+5) - [(n+1)(n+1)]
Multiply out brackets
n²+5n +5n +25 - [n²+n+n+1]

n²+10n+25 - n²-2n -1

=8n+24
= 8(n+3)

[dementedpixie]

B is very similar
(n-3)² - (n+1)(n-1)
(n-3)(n-3) - (n+1)(n-1)
Multiply out brackets

n²-3n-3n+9 - [n²+n-n-1]
n² -6n +9 -n²-n+n + 1
Work along the calculation cancelling out and adding/subtracting
n² cancels out leaving
-6n +10
= 10-6n
= 2(5-3n)

[Wiltinglillies]

I wasn't multiplying out properly.
Thanks.