SOLUTION: Can you help me with this? I am lost as to how to determine the a(1) before I solve. Thank you in advance. Find the sum of the arithmetic sequence having the data given. a(n)=5,

Algebra ->  Sequences-and-series -> SOLUTION: Can you help me with this? I am lost as to how to determine the a(1) before I solve. Thank you in advance. Find the sum of the arithmetic sequence having the data given. a(n)=5,       Log On


   

Question 309124: Can you help me with this? I am lost as to how to determine the a(1) before I solve. Thank you in advance.
Find the sum of the arithmetic sequence having the data given.
a(n)=5, d=-2, n=12
Tina

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Here's what you know,
a%2812%29=5
d=-2
Here's the general equation.
a%28n%29=a1%2B%28n-1%29%2Ad
Plug in what you know,
a%2812%29=a1%2B%2812-1%29%2A%28-2%29=5
Now solve for a1
a1%2B11%28-2%29=5
a1-22=5
a1=27