Question

Calcule a soma dos termos da PA( -8,-5,-2..., 22)

Answer 1

Resposta:

77

Explicação passo-a-passo:

r = a2 - a1 = -5 - (-8) = 3

an = a1 + (n-1).r => 22 = -8 (n-1) 3 => n = 11

Sn = (a1 + an)$\frac{n}{2}$

Sn = (-8 + 22). 11/2 = 77

Answer 2

Sn= (A1+an)n
___------------
______2

Sn=(-8+22).n
___-------------
_____2
Sn= (-8+22).11
____------------
_______2

Sn= 14.11
____-----
_____2

Sn=154/2
Sn= 77

an= A1+(n-1).r
22= -8+(n-1).r
22= -8+(n-1).3
22= -8+(3n-3)
22= -8+3n-3
22+11= 3n
n= 33/3
n= 11


r= a2-a1
r= -5-(-8)
r= -5+8
r= 3