Question

PLEASEEE HELP PLEASSE URGENT.(MEDAL+FAN)
1.What is the common difference of a 57-term arithmetic sequence where the first term is -25 and the sum is 17,727? (1 points)
11
11.5
12
12.5

2.What is the sum of a 14-term arithmetic sequence where the last term is 30 and the common difference is -5? (1 points)
875
812.5
455
422.5

3.When finding the sum of the arithmetic sequence 4 + 1 + -2 + -5 + -8 + -11, you will have a step of work that contains the number -3. Use complete sentences to describe how the -3 was calculated and what it means.

Answer 1

@satellite73 @hartnn @Hero , Can Yall Please Help & Explain Please This IS Urgent

Answer 2

which one ?

Answer 3

1

Answer 4

\(\Large S_n = (n/2) [2a_1 +(n-1)d]\)

here,
Sn = 17727
a1 = -25
n = 57
just plug in values!
only d is unknown

Answer 5

so it'sgoing to b 17727=(57/2)[2(-24)+(57-1)d]

Answer 6

a1 is actually -25, not -24

Answer 7

oh yea so i solve it now rite

Answer 8

yes! simplify and get the value of d :)

Answer 9

I Can't put it into thecalculator norsolve it like its set up

Answer 10

multiply both sides by 2/57 first

Answer 11

left side = 17727*2/57 = ...

Answer 12

622

Answer 13

correct

right side = -50 +56 d

now add 50 on both sides

Answer 14

622 +50 = 56d

can you find d now ?

Answer 15

yeah

Answer 16

good :)

Answer 17

d=12

Answer 18

absolutely correct :)

Answer 19

Thank You So Much. But Can U help me set up the equations for the 2.PLEASE ^.^

Answer 20

sure

Answer 21

we first need to find the 1st term a1

use the n'th term formula
\(\Large a_n = a_1 + (n-1)d\)

here,
n= 14
an =30
d =-5

plug in!
find a1, its the only unknown

Answer 22

30=a1+(14-1)-5

Answer 23

yup
don't miss the brackets
30=a1+(14-1)(-5)

Answer 24

30 = a1 - 13*5

can u find a1 from here ?

Answer 25

Yea. I Think let me try

Answer 26

I Got 95 :/

Answer 27

a1 = 95 is correct :)

Answer 28

now use the same sum formula i gave you before


a1 = 95
d=-5
n=15

plug these in and find the sum!

Answer 29

try this all the way by yourself first :)

Answer 30

k

Answer 31

15/2 (2*95 + 13*(-5))

did you get this after plugging in ?

Answer 32

sorry

14/2 (2*95 + 13*(-5))

Answer 33

ohh...i wrote n=15,its actually n=14 because we need sum of 14 terms

Answer 34

K Thank YOU SOO SOOO MUCH. YOU THE BEST ! I GOT 875. THANKS A TON AGAIN

Answer 35

875 is correct :)
welcome ^_^