Question

Find a8 for the geometric series with r=2, s8=1020, and a1=4

Answer 1

$a_1=4 \\ r=2 \\ \\ a_n=a_1 \times r^{n-1} \\ a_8=a_1 \times r^7 \\ a_8=4 \times 2^7 \\ a_8=4 \times 128 \\ \boxed{a_8=512}$