Question

Obtenha a soma dos doze primeiros termos da PA em que o primeiro termo é 1
--- e a razao , 3 .
2 ----
2

Answer 1

a_12 = a_1+11r

a_12 = 1+11*3

a_12 = 1+33

a_12 = 34

________________________

S_n = (a_1+a_n)*n / 2

S_12 = (1+34)*12 / 2

S_12 = 35*6

S_12 = 210

Answer 2

Sn= (a1+an)n/2 Sn= (1+ an) 12/2 Sn= (1+an).6 >>>> (1+34).6= 35.6= 210 An=a1+ (n-1)r An= 1+ 11. 3 An= 34 Sn=210