Question

calcule o décimo termo da PG (20,-10,5,...)

Answer 1

$a_n=a_{10}=? \\ a_1=20 \\ n=10 \\ r=q=- \frac{10}{20} =- \frac{1}{2} \\ \\ a_n=a_1.q^{n-1} \\ \\ a_{10}=20.(- \frac{1}{2} )^{10-1} \\ \\ a_{10}=20.(- \frac{1}{2} )^9 \\ \\ a_{10}=20.(- \frac{1}{512} ) \\ \\simplificndo \\ \\ a_{20}=- \frac{5}{128}$