CHAPTER-5 ARITHMETIC PROGESSIONS
QUESTION -5
Find the number of terms in each of the following A.P.
ANSWER:
I. 7, 13, 19, …, 205
For this A.P.,
a = 7
d = a2 − a1 = 13 − 7 = 6
Let there are n terms in this A.P.
an = 205
We know that
an = a + (n − 1) d
Therefore, 205 = 7 + (n − 1) 6
198 = (n − 1) 6
33 = (n − 1)
n = 34
Therefore, this given series has 34 terms in it
For this A.P.,
Let there are n terms in this A.P.
Therefore, an = −47 and we know that,
Therefore, this given A.P. has 27 terms in it.