Question

Determine o n° de termos da P.G (128,64,32,...,1/256)

Answer 1

Use a fórmula do termo geral da PG:

$a_n=a_1*q^{n-1}\\ \\ \frac{1}{256}=128.(\frac{1}{2})^{n-1}\\ \\ (\frac{1}{2})^{n-1}=\frac{1}{256}\div128\\ \\ 2^{1-n}=2^{-15}\\ \\ 1-n=-15\\ \\ n=16$