(its a sigma notation )Given the arithmetic sequence 23,17,11...evaluate

Question

anonymous · Answer

$$\sum_{n=4}^{9} a _{n}$$

amistre64 · Answer

what our common difference between terms?

amistre64 · Answer

23 + c = 17

17+c = 11

what is c?

amistre64 · Answer

once you know c you can determine the values of a4 and a9

then add them up 5 times and divide in half

anonymous · Answer

i'm still confused

anonymous · Answer

where are you getting c from?

amistre64 · Answer

an arithmetic sequence is created by adding a constant value to the last term to get the next term.

all you need to do to find the common term is to work out the addition from one term to the next

amistre64 · Answer

our 1st terms is 23 ; they add some amount to it to get 17

23 + c = 17

anonymous · Answer

so c is constant?

amistre64 · Answer

yes, also known as the common difference between each term since its value never changes

anonymous · Answer

so 6
?

amistre64 · Answer

well, -6 in this case :)

anonymous · Answer

23+-6=17
17+-6=11

amistre64 · Answer

now with that iinformation we can either construct the sequence and add up the 4th to 9th terms

anonymous · Answer

but what do i do next i dnt get the$$\sum_{?}^{?}$$ thing?

amistre64 · Answer

or do some fancier stuff that does the same thing

anonymous · Answer

ignore the questions marks please

anonymous · Answer

so the answer is -6?

amistre64 · Answer

the 4 on the bottom means we start with the 4th term and add up all the terms till we get to the 9th term; since we got a 9 up top

anonymous · Answer

how do i evaluate E

amistre64 · Answer

what are the 4th 5th 6th 7th 8th and 9th terms?

anonymous · Answer

what do you mean 4th terms?

amistre64 · Answer

E is just a notation that tells us we are summing up (adding)  all the terms from the bottom-th to the top-th

amistre64 · Answer

you see that 23 in front of our sequence?

anonymous · Answer

so 9+4?

anonymous · Answer

yeah...

amistre64 · Answer

the 23 is our 1st term in the sequence

do you see that 17 that is right next to it?

anonymous · Answer

yeah so that;s the 2nd and 11 is the 3rd?

amistre64 · Answer

yep; and we know how to find each next term so we just need to find the 4th to the 9th terms

anonymous · Answer

so 4th terms is 5?

anonymous · Answer

and 5th is -1

anonymous · Answer

and so on?

amistre64 · Answer

|dw:1334692046398:dw|

yep

anonymous · Answer

so what do i do next after i have all terms 4th-9th?

amistre64 · Answer

term: 4   5   6    7     8     9
value: 5  -1 -7 -13 -19  -25

add em all up

anonymous · Answer

so -60?