Question

Work out the sum of the first 60 terms of the following arithmetic series:
100 + 94 + 88 +...

Answer 1

`S_(60)=-4620`

Explanation:

`S_n=(n)/(2)[2a_1+(n-1)d]\\ \\S_(60)=(60)/(2)[2(100)+(60-1)(-6)] \\\\S_(60)=30[200+(59)(-6)]\\ \\S_(60)=30[200-354]\\ \\S_(60)=30[-154]\\\\S_(60)=-4620`