Simple algebra

[elfin notch]

It is

[quartz kraken]

the minus sign changes it

no
(n(n-1))/2 == ((n^2)/2)-(n/2) is true but since there's a - in front of (n(n-1))/2, it becomes -((n^2)/2)+(n/2)

yeah no problem

[candid spade]

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