Question

Write the explicit formula for the geometric sequence.

a1 = -5 a2 = 20 a3 = -80

A. an = -5 • (-4)n

B. an = -5(-4)n-1

C. an = -4(-5)n-1

D. an = -5 • (4)n

Answer 1

common ratio= 20/-5=-4

un=a*r^n-1

an=-5*-4^n-1

Answer 2

its the B

do tell the answer :)