# Write the series using summation notation -2 + 4+ -8 + 16 + -32​

Write the series using summation notation -2 + 4+ -8 + 16 + -32​

## This Post Has 10 Comments

1. eddsworldfrantic says:

The formula is
$\frac{a_1(1-r^n)}{1-r}$
a1=first term
n=which term
r=common ratio
we see the common ratio is -2
frs term is 1
and we go to 10th term so n=10

$\frac{1(1-(-2)^{10})}{1-(-2)}$
$\frac{1(1-1024)}{1+2}$
$\frac{1(-1023)}{3}$
-341
the sum is -341

2. mallorynichole19 says:

The next will be 64, -128 each on is * by 2 and switching from pos to neg

3. liln223 says:

-4/2

Step-by-step explanation:

just take 4 and divide it by -2 and youll get the common ratio as-2

Hope it helps

4. zoebenally4526 says:

The answer to this is B.  " -1 , -2 , -4, - 8, -16 , -32

5. chem1014 says:

It's b. -1,-2,-4,-8,-16,-32
because
$a_n=2a_{n-1} \mbox{ where } a_1=-1.\\&10;So\\&10;a_2=2a_1=-2\\&10;a_3=2a_2=-4\\&10;a_4=2a_3=-8\\&10;a_5=2a_4=-16\\&10;a_6=2a_5=-32.$

6. clgnwekgklqwejg8619 says:

you multiply it by -2 each time

Explanation:

positive times negative = negative

negative times negative= positive

7. BrownieMan123 says:

- 32 x -2 = 64

64 x -2 = -128

Step-by-step explanation:

Each item is multiplied by -2

8. shelley3135 says:

-2, 4, -8, 16, -32, 64

9. mgendin says:

Remark

You can find the answer to that by dividing any 2 consecutive terms putting the right one in the numerator and the left one in the denominator.

Forumula

ratio = right/left

right = - 8

left = 4

ratio = -8/4

ratio = -2

Any two numbers would work.

ratio = - 32/16 = - 2

10. getsic says:

Hello,

$u_{1}= -2 \\&10;u_{2}= -2 *(-2)=(-2)^2 \\&10;u_{3}= (-2)^2 *(-2)=(-2)^3 \\&10;u_{4}= (-2)^3 *(-2)=(-2)^4 \\&10;&10;...\\&10;&10;\boxed{u_{n}= (-2)^n} \\&10;&#10;$