Question

What is the 25th term of the arithmetic sequence 9, 15, 21, … ?

Answer 1

The difference is 6 between the terms shown, and the first term is 9. 9 + 6n, so when n is 25, the term is 159.

Answer 2

almost ....

Answer 3

if we start this thing with a 6n, then we have to name our terms one less

so we usually just make things simpler by adjusting the formula instead

Answer 4

\[a_n=a_1+d(n-1)\]