Question

Determine o número de termos da p.a finita
(4,7,10,...,151)

Answer 1

a1=4
r=3
an=151
n=?

an=a1+(n-1).r
151=4+(n-1).3
151=4+3n-3
151-4+3n-3
147+3=3n
150=3n
150/3=50

Portanto essa p.a possui 50 termos!

a sequencia é :
(4,7,10,13,16,19,22,25,28,31,34,37,40,43,46,49,52,55,58,61,64,67,70,73,76,79,82,85,88,91,94,97,100,103,106,109,112,115,118,121,124,127,130,133,136,139,142,145,148,151).
contando vc percebe que tem 50.

Answer 2

an = a1 + ( n - 1 ) r

onde:

a1 = 4

an = 151

r = a2-a1 = 7-4=3

Logo:

151 = 4 + ( n -1 ) . 3

151 = 4 + 3n - 3

-3n = 4-3-151

-3n = 1-151

-3n = -150

n = -150/-3

n = 50