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.

Answer 1

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