Question

quantos termos tem a p.a(2,7,...997). Qual e a soma dos termos desta pa.

Answer 1

r=7-2
r=5

An=A1+(n-1)r
997=2+(n-1)5
997-2/5=n-1
995/5=n-1
199=n-1
199+1=n
n=200 termos.

Sn=(A1+An)n
S200=(2+997)200
S200=999.200
S200=199800 seria a soma.

Answer 2

a1 = 2
a2 = 7
r = 7-2 = 5 ***
an = 997
a1 + ( n-1)r  = 997
a1 + ( n-1)5 = 997
2 + 5n - 5 = 997
5n - 3 = 997
5n = 997 + 3
5n =1000
n = 200 ****
Sn =( a1 + an)* 100
Sn = ( 2 + 997)* 100
Sn = 999 * 100
Sn = 99900