Question

determine a soma dos termos da PRA. A (3,11,19...115)

Answer 1

an = a1 + ( n - 1 )r

115 = 3 + ( n - 1 ) 8

115 = 3 + 8n - 8

115 = - 5 + 8n

115 + 5 = 8n

n = 120/8

n = 15


___________________________________________




Sn = ( a1 + an ) n / 2

Sn = ( 3 + 115 ) 15 / 2

Sn = 118 * 15 / 2

Sn = 1770 / 2

Sn = 885





espero ter ajudado