I dont get how to do this can anyone please help me

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If there is a fraction bar between the "i² +i" term and the "2", then what you have is:

(5² + 5)/2  + (6² + 6)/2 + (7² + 7)/2 + (8² + 8)/2 + (9² + 9)/2 + (10² + 10)/2 + (11² + 11)/2 + (12² + 12)/2

Now, it's between you and your calculator ...