Write an explicit formula for n ​th ​​ term of the sequence 21, 11, 1, ...

Question

I need help with this problem  and thank to anyone that helps me understand. how to do this.

Answer 1

This is an arithmetic sequence because 11 - 21 = 1 - 11. Each term, the value decreases by 10. The starting term is 21, so we build the equation as:

 

a_n = 21 - 10(n-1)

 

"10" is multiplied with "n-1" instead of "n" because we established 21 as the first part of the equation.

 

If we want to identify the first term in the sequence, we substitute "1" for "n" a_1 = 21 - 10(1-1) = 21 - 0 = 21.