Pls someone help me:
{Xn },n = 0,1,2,3, is an arithmetic sequence such that the 7th term minus the 4th term is 12 and the sum of the 7th term and 4th terms is -28.Obtain the closed form of the sequence and write down the 10th and 20th term.
Tks
Pls someone help me:
{Xn },n = 0,1,2,3, is an arithmetic sequence such that the 7th term minus the 4th term is 12 and the sum of the 7th term and 4th terms is -28.Obtain the closed form of the sequence and write down the 10th and 20th term.
Tks
Hello, watcher!
You're expected to know this formula . . .There is an arithmetic sequence such that the 7th term minus the 4th term is 12
and the sum of the 7th term and 4th terms is -28.
Obtain the closed form of the sequence and write down the 10th and 20th terms.
The term is: .
. . where is the first term, and is the common difference.
The term is: .
The term is: .
Their difference is 12: .
Their sum is -28: .
. . Substitute [1] into [2]: .
Hence, the term is: .
The term is: .
The term is: .
Thanks a lot. But I have a question though and am confused and curious to know (am not so good in math).
Since n starts with zero, why was the formula of Xn = a + (n-1)d used in this problem - and not the closed form of Xn = a + nd (n = 0, 1, 2, ...)?
Thanks again for your help.