Q8 of 89 Page 49

Justify whether it is true to say that the following are the nth terms of an AP.

Put n = 1, 2, 3, 4


We get


a1 = 3(1)2 + 5 = 8


a2 = 3(2)2 + 5 = 17


a3 = 3(3)2 + 5 = 32


a4 = 3(4)2 + 5 = 53


List of AP is 8, 17, 32, 53. . . .


a2 - a1 = 17 - 8 = 9


a3 - a2 = 32 - 17 = 15


As


a3 - a2 is not equal to a2 - a1


the list is not an AP


More from this chapter

All 89 →
7

In which of the following situations, do the lists of numbers involved from an AP? Give reasons for your answers.

(i) The fee charged from a student every month by a school for the whole session, when the monthly fee is Rs 400.


(ii) The fee charged every month by a school from classes I to XII, when the monthly fee for class I Rs 250 and it increase by Rs 50 for the next higher class.


(iii) The amount of money in the account of Varun at the end of every year when Rs 1000 is deposited at simple interest of 10% per annum.


(iv) The number of bacteria in a certain food item after each second, when they double in every second.

 8

Justify whether it is true to say that the following are the nth terms of an AP.

2n – 3

 8

Justify whether it is true to say that the following are the nth terms of an AP.

1 + n + n2

 1

Match the AP’s given in column A with suitable common differences given in column B.




















































Column A




Column B



(A1)



2, - 2 – 6, - 10, …



(B1)





(A2)



a = - 18, n = 10, an = 0



(B2)



–5



(A3)



a = 0, a10 = 6



(B3)



4



(A4)



a2 = 13, a4 = 3



(B4)



–4





(B5)



2





(B6)







(B7)



5