Chapter 8
Predicting What Comes Next: Exploring Sequences and Progressions
CBSE Class 9
Mathematics Solutions
Educart Mathematics class Class 9 NCERT Exemplar cover
Question:

Find the first five terms of the sequence in which the nthn^{\text{th}} term is given by

(A) tn=3n4t_n = 3n - 4, (B) tn=25nt_n = 2 - 5n, and (C) tn=n22n+3t_n = n^2 - 2n + 3, for n1n \geq 1.                       [Page No. 179]

Answer: Verified

(A) tn=3n4t_n = 3n - 4:

t1=3(1)4=1t_1 = 3(1) - 4 = -1

t2=3(2)4=2t_2 = 3(2) - 4 = 2

t3=3(3)4=5t_3 = 3(3) - 4 = 5

t4=3(4)4=8t_4 = 3(4) - 4 = 8

t5=3(5)4=11t_5 = 3(5) - 4 = 11

First five terms: -1, 2, 5, 8, 11

(B) tn=25nt_n = 2 - 5n

t1=25=3t_1 = 2 - 5 = -3

t2=210=8t_2 = 2 - 10 = -8

t3=215=13t_3 = 2 - 15 = -13

t4=220=18t_4 = 2 - 20 = -18

t5=225=23t_5 = 2 - 25 = -23

First five terms: -3, -8, -13, -18, -23

(C) tn=n22n+3t_n = n^2 - 2n + 3:

t1=12+3=2t_1 = 1 - 2 + 3 = 2

t2=44+3=3t_2 = 4 - 4 + 3 = 3

t3=96+3=6t_3 = 9 - 6 + 3 = 6

t4=168+3=11t_4 = 16 - 8 + 3 = 11

t5=2510+3=18t_5 = 25 - 10 + 3 = 18

First five terms: 2, 3, 6, 11, 18

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