Question

What is the sum of the terms of the series (-1) + (-2) + (-3) +... + (-10)?

A. -110

B. -55

C. -22

Answer 1

`S_(10)=-55`

Explanation:

The given series is

`(-1)+(-2)+(-3)+...+(-10)`

The first term of this arithmetic sequence is

`a_1=-1` the last term is
`l=-10`

The sum of the first n-terms is given by

`S_n=(n)/(2)(a_1+l)`

The first 10 terms is

`S_(10)=(10)/(2)(-1+-10)`

`S_(10)=5(-11)`

`S_(10)=-55`