Question

The first term in an arithmetic sequence is 9 and the tenth term is 45. Use the first and tenth terms to find the sun of the first 10 terms. The equation of the sequence is an=4n+5

Answer 1

270.

Explanation:

If the first term = a and 10th term = a + 9d where d = the common difference.

a + 9d - a = 45 - 9

9d = 36

d = 4.

Sum of first 10 terms = (10/2)[2*9 + (10-1)*4]

= 5 * (18 + 36)

= 5 * 54

= 270.