Question

3) The sum of first 13 terms and the sum of next 12 terms of an arithmetic sequence areequal. If its common difference is 3.-a) How many times of the common difference will be the difference between 1 and firstterms of this sequence ?b) What is the 13 term of this sequence ?c) What is the sum of first 25 terms of this sequence?​

Answer 1

Use the value of the common difference d=3 and the first term a

1

=6 in the formula for the nth term given above.

a

n

=a

1

+(n−1)d

=6+3(n−1)

=3n+3

The 50

th

term is found by setting n=50 in the above formula.

a

50

=3(50)+3=153