Question

Determine o primeiro termo da p.g em que a6=128 e q=2

Answer 1

a1 = ...
a6 = 128
q = 2
a6 = a1.q^(n-1)
128 = a1.2^(6-1)
2^7 = a1.2^5
a1 = 2^7/2^5
a1 = 2²
a1 = 4

Answer 2

$a_1=?\\ a_6=128\\ n=6\\ q=2\\\\\\ a_n=a_1*q^{n-1}\\\\\\ 128=a_1*2^{6-1}\to \\\\ 128=a_1*2^{5}\to \\\\ 128=a_1*32\to \\\\ \frac{128}{32} =a_1\to \\\\a_1=4\\\\\\\\ PG(4,8,16, 32, 64, 128)$