Question

Which of the following choices is the explicit formula for the following geometric sequence?

-0.1, 0.04, -0.016, 0.0064, -0.00256, ...

A. an = 0.1(0.4)n
B. an = 0.1(-0.4)n-1
C. an = 0.4(-0.4)n-1
D. an = -0.1(-0.4)n-1
E. an = -0.1(0.4)n-1

Answer 1

@magepker728 could you help me out one more time?

Answer 2

or @ShadowLegendX

Answer 3

@Nnesha

Answer 4

do you know the original formula ??

Answer 5

well its \[\huge\rm a _{n}=a _{1} \times r ^{n-1}\]

Answer 6

where a1 us first term
and r is ratio

Answer 7

r is also in parantheses as well as n-1

Answer 8

n-1 is exponent of r

Answer 9

first tell me what is first term ??

Answer 10

an=-0.1?

Answer 11

yes not an
a1 = -0.1

Answer 12

did you notice first term is negative and second term is positive so what your ratios suppose to be(all answer choices have same ratio but different sign )
so see which one is right
is it -.4 or positive .4 ??

Answer 13

it should be a positive 0.04

Answer 14

yes right so replace r by 0.4 and a1 by -0.1
in the formula that i gave you

Answer 15

an=0.1(0.04)^(n-1)
right?

Answer 16

nope your first term is negative

Answer 17

an=-0.1(0.04)^(.-1)
how bout now?

Answer 18

anh

Answer 19

nope

Answer 20

exponent is n-1

Answer 21

(n-1) i think i hit the wrong button on that one

Answer 22

yes then that's right

Answer 23

so it would be D

Answer 24

yes right

Answer 25

wait

Answer 26

nope

Answer 27

actually not. its gotta be both negative

Answer 28

yeah that's right ^

Answer 29

btw yes it is D
i thought you just have 4 choices and D is E but
there is 5 answer chocies

Answer 30

@Tallan so yeas D is right answer
bec ratio is negative .4

Answer 31

@Tallan did you get this one

Answer 32

i got it yea... Could you help me with the other problem i posted?

Answer 33

okay :)