Question

calcule a soma dos oitenta primeiros termos da p.a.(6,9,12,15,18)

Answer 1

an= a1 +( n-1). R
An= 6+(80-1) .3
An= 6+(79).3
An = 243

Sn= (a1+ an) .n /2
Sn= 6+243.80 /2
Sn = 9723