SOLUTION: The fourth term of an arithmetic progression is 20. The common difference is 4. Find the first term of the sequence. Can someone explain in detail step by step how to get the ans

Algebra ->  Finance -> SOLUTION: The fourth term of an arithmetic progression is 20. The common difference is 4. Find the first term of the sequence. Can someone explain in detail step by step how to get the ans      Log On


   

Question 1027002: The fourth term of an arithmetic progression is 20. The common difference is 4. Find the first term of the sequence.
Can someone explain in detail step by step how to get the answer please
Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
By definition of an arithmetic progression,
a%5Bn%5D=a%5B1%5D%2B%28n-1%29%2Ad
.
.
a%5B4%5D=a%5B1%5D%2B%284-1%29%2Ad
.
.
Substituting,
20=a%5B1%5D%2B%284-1%29%2A4
20=a%5B1%5D%2B3%2A4
20=a%5B1%5D%2B12
highlight%28a%5B1%5D=8%29
So then,
a%5Bn%5D=8%2B%28n-1%29%2A4
a%5Bn%5D=8%2B4n-4
highlight%28a%5Bn%5D=4%2B4n%29
a%5B1%5D=8
a%5B2%5D=12
a%5B3%5D=16
a%5B4%5D=20