Question

An arithmetic sequence has a 10th term of 15 and 14th term of 35.

What is the value of the first term? Use the value of d in one of the sequence equations from a.

Answer 1

10 th term= 15

a+ 9d = 15......(1)

14 th term = 35

a+ 13d = 35.....(2)

(2)-(1)

4d= 20

d= 5

put d= 5 in eq1

a+9d=15

a+9(5) = 15

a+45= 15

a= -30