Question

. Find the 20th term of the arithmetic sequence 15, 9, 3, -3

Answer 1

Answer:

a20 = -99

Step-by-step explanation:

hello :

the nth term in this  arithmetic sequence is : an = a1 + (n -1 )d

a1 = 15   a2 = 9       d = a2-a1 = 9-15 = -6  ( common difrence)

an = 15 + (n -1 )(-6)

an = 15+6-6n

an = -6n+21

the 20th term when n = 20 :  a20 = -6(20)+21 = -99