Question

Write the sum using summation notation, assuming the suggested pattern continues.

-9 - 3 + 3 + 9 + ... + 81

Answer 1

@surjithayer

Answer 2

it is an A.P.
a=-9
d=-3-(-9)=-3+9=6
find n by the the formula
\[l=a+(n-1)d\]
can you find n
l=81

Answer 3

are you here?

Answer 4

these are answer options
find n

Answer 5

i did A @surjithayer

Answer 6

i want to know how?
can you show me ?

Answer 7

@surjithayer i guessed im sry i suck at math

Answer 8

ok.

Answer 9

81=-9+(n-1)*6
81+9=(n-1)6
\[\frac{ 90 }{ 6 }=n-1\]
n-1=15
n=15+1=16

Answer 10

you got it.

Answer 11

but on all of them n=0

Answer 12

wait is it d?

Answer 13

that means there are 16 terms for n=0,1,2,...,15

Answer 14

here for A ,n=0
a1=-9
a2=-9+6*1=-3
a3=-9+6*2=3
.....
a16=-9+6*15=81

Answer 15

I said A in the first place @surjithayer

Answer 16

A is correct. as i have shown.

Answer 17

would you like to see how sum of arithmetic series formula comes

Answer 18

could u show me on this one?
Write the sum using summation notation, assuming the suggested pattern continues.
5 - 15 + 45 - 135 + ...

Answer 19

it is a G.P.
can you find r?

Answer 20

what is gp, i need it in summation notation

Answer 21

gp means geometric progression

Answer 22

for that you have to find r(common ratio)

Answer 23

\[r=\frac{ t _{n} }{ t _{n-1} }\]
to be precise 2nd term/1st term

Answer 24

@surjithayer what one did u get as the answer

Answer 25

\[r=\frac{ 45 }{ -15 }=?\]

Answer 26

\[r=\frac{ -15 }{ 5 }=\frac{ 45 }{ -15 }=?\]

Answer 27

@surjithayer its b right?

Answer 28

r=-3
B is correct.