Question

After solving the next three terms in
5120, 1280, 320, 80, …
How could you find the explicit rule?

Answer 1

a (n)=a1 × r^(n-1)

a1=5120

a2=1280

a3=320

a4=80

-->a2/a1=1280/5120=0.25

-->a3/a2=320/1280=0.25

-->a4/a3=80/320=0.25

ration(r) =0.25

■■■a(n)=a1 × r^(n-1)■■■

a (5)=5120×0.25^(5-1)

a (5)=5120 × 0.25 ^(4)

a (5) = 5120 × 0.00390625

a (5) = 20