The second term of an arithmetic sequence is 7. The sum of the first four terms of the sequence is 12. Find the first term, a, a
nd the common difference, d, of the sequence.
2 answers:
T2 = 7
S4 = 12
7 = a + 6d
a = 7 - 6d
12 = 2 ( 2(7-6d) +3d )
6 = 14 - 12d + 3d
9d = 8
d = 8/9
a = 7 - 6(8/9)
a = 1/2/3
Are you sure its Arithmetic?
There isn't a way to solve this, that sum of the first four terms has got me a little screwed up.
the formula you want to use is this:
An=A1+D(N-1)
A1 is the first term of the sequence D is a common difference and N is the term of the sequence.
7= 1 + 6 (2-1)
that's the only way, so let's plug it in for the first one 3rd and 4th
A1= 1 + 6 (1-1)
A1=1
A3= 1 + 6 (3-1)
A3=13
A4= 1 + 6 (4-1)
A4=19
that's as far as I can help, though.
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