Find a1, for the arithmetic series with S14 = - 420 and d = -6.
Mathematics · Middle School · Thu Jan 21 2021
Answered on
Given:
S14 = -420
d = - 6
Determine a1
Formula for arithmetic sequence:
An = a1 + (n-1)d
Solution:
Substitute the given values of An and d to the formula and solve for a1.
-420 = a1 + (14 - 1) -6
-420 = a1 + (13) -6
-420 = a1 + (-78)
-420 = a1 - 78
Transpose -78 on the other side of the equation, hence it must be taken to note that in transposing a number, the sign changes.
a1 = -420 + 78
a1 = -342
Final answer:
a1 = -342