The sum of the first 12 terms of an arithmetic sequence is 228. The common difference is 4. What are the first 3 terms?

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Answer 1 · 2018-03-29T03:49:47

#a_1 = -3#

#a_2 = 1#

#a_3 = 5#

I am using information from this reference Arithmetic Progression

An equation of the sum of n terms of an arithmetic progression is:

#S_n = n/2(2a_1+(n-1)d)#

We are given that #S_12 = 228# and #d = 4#; this allows us to find the value of #a_1#

#S_12 = 228 = 12/2(2a_1+(12-1)4)#

#228 = 12a_1+(11)24#

#12a_1=-36#

#a_1 = -3#

For the next terms, add 4 to each preceding term:

#a_2 = 1#

#a_3 = 5#