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

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

anonymous · Answer

Here is another one, I have no idea what this stuff is.  Write the recursive formula for the geometric sequence.

a1 = -2  a2 = 8  a3 = -32
	A. an = -4 + an-1
	
	B. an = -2 + an-1
	
	C. an = -2 • an-1
	
	D. an = -4 • an-1


Its the last one on the test, though.  So thats good.

anonymous · Answer

Do you need to know the difference between recursive and explicit formulas?

anonymous · Answer

Um.... I'm not sure.  I'm trying to do this test without the textbook - my school won't let me have it until my teacher grades my final exam on Algebra 1 part 1.

anonymous · Answer

I don't really care about learning it right now, so long as I can get the correct answer on these.  I'll just learn it when I get the textbook.

anonymous · Answer

ok. To be sure, an explicit formula expresses every term of a sequence or series as some operation on a variable. A recursive formula "returns" to a previous term to find the next one. A good policy is to test each of the given answers by substituting. It can take time, but it's worth it.