Explicit equations for arithmetic sequences follow a specific format.
a_n= a_1+( n-1) d
In this form, a_1 is the first term in a given sequence, d is the common difference from one term to the next, and a_n is the nth term in the sequence. For this exercise, the first term is a_1= 3. Let's observe the other terms to determine the common difference d.
3+6 →9+6 →15+6 →21...
By substituting these two values into the explicit equation and simplifying, we can find the formula for this sequence.