Question

numa p.a a1= -3 e r = 5 . calcule a soma dos 20 primeiros termos dessa p.a

Answer 1

a1 = -3 r = 5 n = 20
an = a1+(n-1).r
an = -3+(20-1).5
an = -3+19.5
an = -3+95
an = 92
Sn = (a1+an).n/2
Sn = (-3+92).20/2
Sn = 89.10
Sn = 890