Question

Determine a soma dos cinco primeiros termos da P.A (10,20,30,40,...)
A)120
B)140
C)150
D)200
Cálculos

Answer 1

a1= 10 n=5 r= 20-10= 10
an= a1 + (n-1) × r
an= 10 + (5-1) × 10 ← 5×10 e 1×10
an= 10 + 40
an= 50

Sn= (a1+an) × n /2 ← sobre 2
S5= (10+50) × 5 ← 10×5 e 50×5 /2
S5= 50+250 /2
S5= 300/2
S5= 150 (letra c)