Question

15 pontos!

Encontre o a1 de uma PG cujo a6= 5 e q= $\frac{1}{2}$

Answer 1

Olá.

Basta usarmos o termo geral da P.G.
$\mathsf{a_n=a_1\cdot q^{n-1}}\\\\ \mathsf{a_6=a_1\cdot\left(\dfrac{1}{2}\right)^{6-1}}\\\\ \mathsf{5=a_1\cdot\left(\dfrac{1}{2}\right)^{5}}\\\\ \mathsf{5=a_1\cdot\dfrac{1}{2^5}}\\\\ \mathsf{5=\dfrac{a_1}{32}}\\\\ \mathsf{5\cdot32=a_1}\\\\ \boxed{\mathsf{160=a_1}}$

Qualquer dúvida, deixe nos comentários.
Bons estudos.