Question

Write a formula for the general term​ (the nth​ term) of the arithmetic​ sequence, a 1 comma a 2 comma a 3 comma a 4 . . . . ​then, use the formula for a subscript n to find a 20​, the 20th term of the sequence. 7​, 5​, 3​, 1​, ... a subscript nequals nothing

Answer 1

We have an initial term of 7 and a common difference of -2, so

a_n = 7 + -2(n-1) = -2n + 9

a_20 = -2(20)+9 = -40 + 9 = -31