find the partial sum
100
∑ 6n
n=10
ok this is what i did but i didnt get the same answer as the book can someone tell me what i did wrong please?
100
∑ 6n
n=10
60+66+72+78+...
a1=60 d=66-60--> d=6
c=a1-d --> c=60-6 --> c= 54
an= dn+c --> an= 6n+54 --> a100=6(100)+54 --> a100= 654
Sn= n/2(a1+an) --> Sn=100/2(60+654) --> Sn= 35700 which is the wrong answer......aarrrrrrrrrrrrrrrrhhhhh
i looked in the back of the book and the correct answer is 30,030. what did i do wrong?