Question

4- Calcule o 64° termo da PA ( 19,17,15,13,...)?

5- Quantos termos tem a PA ( 5, 8, 11, ...,224)?

Answer 1

a 64 = ?
P.A.(19,17,15,13,.......)
A 1 = 19
A 2 = 17
R = A 2 - A 1
R = 17 - 19
R = -2
a 64 = a 1 + (n - 1 ).-2
a 64 = 19 + (64 - 1 ).-2
a 64 = 19 + (63).-2
a 64 = 19 - 126
a 64 = -107

P.A.(5,8,11,....224)
n = ?
a 1 = 5
a 2 = 8
r = a 2 - a 1
r = 8 - 5
r = 3
a n = 224
a n  = a 1 + (n - 1 ).3
224 = 5 + 3 n - 3
224 = 2 + 3 n
224  - 2 = 3 n
222 = 3 n
222/3 = n
n = 74

Possui 74 termos