Question

The 50th term of an arithmetic sequence is 86 and the common difference is 2.  Find the first three terms of the sequence.

Answer 1

$a_n=a_{n-1}+d=a_{n-2}+2d=\cdots=a_1+(n-1)d$

which means

$a_{50}=86=a_1+49\times2\implies a_1=-12$

which in turn means the next two terms are $a_2=-10$ and $a_3=-8$.