Question

Write the explicit formula for the geometric sequence.

a1 = -5 a2 = 20 a3 = -80

Answer 1

A. an = -5 • (-4)n

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

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

D. an = -5 • (4)n

Answer 2

What say you? Try them out by producing those three values.

Answer 3

I don't really know how to do these. I didn't get much time to study... Could you explain?

Answer 4

Use the value n = 1 in each description. See which produce -5

A. an = -5 • (-4)n
a1 = -5*(-4)^1 = -5*-4 = 20 -- That's not -5

B. an = -5(-4)n-1
a1 = -5(-4)^0 = -5*1 = -4 -- Okay, this one is in the running

C. an = -4(-5)n-1
a1 - -4(-5)^0 = -4*1 = -4 -- That's not -5

D. an = -5 • (4)n
a1 = -5(4)^1 = -6*4 = -20 -- That's not -5

Looks like you need to try "B".

What is a2?
What is a3?

Do we have a complete match?

Answer 5

I'm still not understand.