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deepaksoni
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Asked: 2021-05-09T22:01:50+05:30 In:

Problem 2: Show that the sequence defined by an = 3n2 – 5 is not an A.P.

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This is the basic and conceptual question from Chapter name- Arithmetic Progression
Chapter number- 9
Exercise 9.2
In this question we have to. Prove that the sequence defined by an = 3n2 – 5 is not an A.P by using arithmetic progressions properties.

CBSE DHANPAT RAI publications
Class:- 10th
Understanding CBSE Mathematics
Question 2

class 10rd sharma
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    1. Guru

      Solution:

      Given: 

      an = 3n2 – 5

      Now putting n = 1, 2, 3, 4 we get,

      a1 = 3.1.1 – 5= 3 – 5 = -2

      a2 = 3.2.2 – 5 = 12 – 5 = 7

      a3 = 3.3.3 – 5 = 27 – 5 = 22

      a4 = 3.4.4 – 5 = 48 – 5 = 43

      We can see that,

      a2 – a1 = 7 – (-2) = 9

      a3 – a2 = 22 – 7 = 15

      a4 – a5 = 43 – 22 = 21

      Since, the successive difference of list is not the same

      ∴ The given sequence is not in A.P 

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