A community for students.
Here's the question you clicked on:
 0 viewing
anonymous
 5 years ago
please help
The 11th term of an arithmetic progression is 1. the sum of the first 10 terms is 120.
find the 4th term :S
formula for the...
sum of terms=1/2n(a+l)=1/2n{2a+(n1)d}
thanks
anonymous
 5 years ago
please help The 11th term of an arithmetic progression is 1. the sum of the first 10 terms is 120. find the 4th term :S formula for the... sum of terms=1/2n(a+l)=1/2n{2a+(n1)d} thanks

This Question is Closed

Yuki
 5 years ago
Best ResponseYou've already chosen the best response.1\[{11(a_1 + a_{11}) \over 2} = 120 + 1 \]

Yuki
 5 years ago
Best ResponseYou've already chosen the best response.1so\[{a_1 + 1} = 22\] thus a_1 = 21

Yuki
 5 years ago
Best ResponseYou've already chosen the best response.1Then you can say\[a_{11} = a_1 + 10d\] \[a_11 = 1 = 21 + 10d\]

Yuki
 5 years ago
Best ResponseYou've already chosen the best response.1that means that the 4th term is 21+3(2) = 15

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0but you didnt even use 4 once :S??? and i dont really understand where 21+3(2)=15 comes from :(

Yuki
 5 years ago
Best ResponseYou've already chosen the best response.1ok, \[a_n = a_1 + d(n1)\] so\[a_4 = a_1 + (2)(41) = 21 + 3(2)\]

Yuki
 5 years ago
Best ResponseYou've already chosen the best response.1the idea of arithmetic sequence is that you are "Adding the same number for all sequence"

anonymous
 5 years ago
Best ResponseYou've already chosen the best response.0sorry but i first thought that i knew where 11(a1+a11)2=120+1 came from but i dont :S

Yuki
 5 years ago
Best ResponseYou've already chosen the best response.1the first ten numbers add up to 120, so 10(a1+a10) /2= 120 now if you add a11 to it, it is 120 + 1 but adding a11 to the sum from a1 to a10 is as same as adding from a1 to a11 so 11(a1 + a11)/2 = 121
Ask your own question
Sign UpFind more explanations on OpenStudy
Your question is ready. Sign up for free to start getting answers.
spraguer
(Moderator)
5
→ View Detailed Profile
is replying to Can someone tell me what button the professor is hitting...
23
 Teamwork 19 Teammate
 Problem Solving 19 Hero
 Engagement 19 Mad Hatter
 You have blocked this person.
 ✔ You're a fan Checking fan status...
Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.