Question

If the fourth term of an arithmetic sequence is 18 and twentieth term is 98, find the first term (a) and the common difference (d)

Answer 1

Answer: First Term = -12 ; Common difference = 10


Step-by-step explanation:

a4 = a1 + 3d ==========> 18 = a1 + 3d
a12 = a1 + 11d==========> 98 = a1 + 11d

8d = 80
d =10 <<<<<<<<<<<<< ¯\_(ツ)_/¯ We found the common difference

18 = a1 + 3(10)
18 = a1 + 30
a1 = -12 <<<<<<<<<<<<< ¯\_(ツ)_/¯ We found the first term