Question

find the arithmetic sum 76 + 71 + 66 + … + (−104).

Answer 1

The arithmeic sequence

Formula for n th term in arithmeic sequence

Where d  = Common difference , a  = first term

In this case

 a  = 76

 

Substitute a = 76 , d = -5,   values in n th term.

Formula for arthmetic sum

Where a = First term , l = last term .

Substitute the values of a = -5, l  = -104 and n  = 37.

Arthmetic sum of is -518.