Question

Determine a soma dos n termos da (13;20;27;............335)​

Answer 1

r= A2 - A1 = 7

an= A1 + (n-1) . r

335= 13 + (n-1).7

335= 13 + 7n - 7

335 -13 +7 = 7n

329= 7n

329/7 = n

47 = n

Sn= (A1+ A2) . n/2

Sn= (13 + 335).47/2

Sn= 348.47/2

Sn = 16356/2

Sn= 8178