Question

The first four terms in an arithmetic sequence are -3, -10, -17, and -24. Which expression can be used to find the nth term ? What is the 25th term of the sequence?
A) -7(n - 1); -168
B) -3 + (n - 1)(-7); -171
C) -3 + (n + 1)(-7); -185
D) 3 + (n - 1)(-7); -165

Answer 1

Hello : 
the nth term is : An = A1 +(n-1)d     d :common difference  A1: the first term
d=(-24)-(-17) = (-17)- (-10) = (-10) -(-3) =-7  and A1 = -3
An = -3 +(n-1)(-7)........(B) -3 + (n - 1)(-7))
A25=-3+(25-1)(-7)=-3-168 = -171