Question

If for an A.P, S15 = 225 and t15 = 20, then a =?​

Answer 1

Step-by-step explanation:

GIVEN :

S15 = 225

T15 = 20

TO FIND :

VALUE OF a.

SOLUTION :

SOLUTION IS EXPLAINED IN THE DIAGRAM.

ANSWER :

a = FIRST TERM IS 10.

Answer 2

Step-by-step explanation:

We know that the formula for the nth term is t

n

=a+(n−1)d, where a is the first term, d is the common difference.

It is given that the nth term is t

15

=55 and the first term is a=13, therefore,

t

n

=a+(n−1)d

⇒55=13+(15−1)d

⇒55=13+14d

⇒14d=55−13

⇒14d=42

⇒d=

14

42

=3

Hence, d=3