WILL FAN AND GIVE MEDAL, PLS HELP. What is the 9th term of the geometric sequence 4, -20, 100, ...?

Question

anonymous · Answer

A. -312,500	
	B. -12,500	
	C. 62,500	
	D. 1,562,500

turingtest · Answer

what is the pattern to get from one term to the next?

anonymous · Answer

-5

turingtest · Answer

great, so the formula for the nth term in the sequence $a_n$ would be what?

secret-ninja · Answer

Just multiply the number -5 9 times. :p

secret-ninja · Answer

4 x -5 = -20
                -20 x -5 = 100 
                100 x -5 = -500
                -500 x -5 = 2500
                2500 x -5 = -12500
                -12500 x -5 = 62500 
                62500 x -5 = -312500
                -312500 x -5 = 1562500

secret-ninja · Answer

There  :)

secret-ninja · Answer

Do you understand?

turingtest · Answer

or you can figure out that the formula for the nth term is$$a_n=4(-5)^{n-1}$$and just plug in for n=the term you want

anonymous · Answer

That's not one of the answers so no.

anonymous · Answer

Oh never mind, yes it is

secret-ninja · Answer

Yep, @TuringTest used the easy way. :)

secret-ninja · Answer

Formulas are faster, but I take time :p lol

anonymous · Answer

Thank you so much!