Let Sn be the sum of the first n terms of an arithmetic sequence, whose first three terms are u1, u2 and u3. It is known that S1 = 7, and S2 = 18.
(a) Write down u1.
(b) Calculate the common difference of the sequence.
(c) Calculate u4.

Question

Let Sn be the sum of the first n terms of an arithmetic sequence, whose first three terms are u1, u2 and u3. It is known that S1 = 7, and S2 = 18.
(a)	Write down u1.
(b)	Calculate the common difference of the sequence.
(c)	Calculate u4.

jdoe0001 · Answer

$\Large a_n = a_1+(n-1)d\
\textit{d = common ratio}\
n=\textit{ the nth term}\
a_1 =\textit{the 1st term}$