Question

qual o primeiro termo de uma pg com 8 termos aonde o ultimo vale -1 e a razao 1/2?

Answer 1

$a_1=?\\n=8\\ q= \frac{1}{2} \\ a_n=-1\\\\\\a_n=a_1*q^{n-1}\\\\\\-1=a_1* \frac{1}{2} ^{8-1}\to \\\\ -1=a_1* \frac{1}{2} ^{7}\to \\\\ -1=a_1* \frac{1}{128}\to \\\\ \frac{-1}{\frac{1}{128}} =a_1\to \\\\ -1*128=a_1\to \\\\ a_1=-128$


$PG(-128,-64,-32,-16,-8,-4,-2,-1)$