Write the explicit formula that represents the geometric sequence -2, 8, -32, 128. what am i supposed to do with the negative numbers? im so confused, please help

Question

myininaya · Answer

what is the common ratio?

myininaya · Answer

just take a term and divide it by it's previous term to find

anonymous · Answer

would it be 4?

myininaya · Answer

well 8/-2 is -4 actually

myininaya · Answer

$$a_n=ar^{n-1}$$

myininaya · Answer

replace r with -4

anonymous · Answer

so is  that how you found the common ratio?

myininaya · Answer

yep just take a term and divide it by it's previous term

anonymous · Answer

xn = 8 × -2(n-1)?

anonymous · Answer

8 x -4

myininaya · Answer

$$a_n=a \cdot r^{n-1 } \ r \text{ is common ratio number } \ a \text{ is first term in the sequence }$$

anonymous · Answer

so is that all you have to do? or do you ri==write out an equation for it?

myininaya · Answer

$$a_n=a \cdot r^{n-1 } \ r \text{ is common ratio number } \ a \text{ is first term in the sequence }$$
all you do is replace r with -4 
and a with the first number in the sequence

myininaya · Answer

do you see what your first number is in your sequence?

anonymous · Answer

okay thanks!

myininaya · Answer

we have a=-2 and r=-4
so our formula is:
$$a_n=(-2) \cdot (-4)^{n-1} $$