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

Suppose W1=1W_{1} = 1, W2=2W_{2} = 2 and for n>2n > 2, Wn=W1+W2++Wn2+2W_{n} = W_{1} + W_{2} + \dots + W_{n-2} + 2.
Find the values of W1,W2,,W8W_{1}, W_{2}, \dots, W_{8}. Do you recognise this sequence?

Answer: Verified

W1=1W_1 = 1

W2=2W_2 = 2

W3=W1+2=1+2=3W_3 = W_1 + 2 = 1 + 2 = 3

W4=W1+W2+2=1+2+2=5W_4 = W_1 + W_2 + 2 = 1 + 2 + 2 = 5

W5=W1+W2+W3+2=1+2+3+2=8W_5 = W_1 + W_2 + W_3 + 2 = 1 + 2 + 3 + 2 = 8

W6=W1+W2+W3+W4+2W_6 = W_1 + W_2 + W_3 + W_4 + 2

=1+2+3+5+2=13= 1 + 2 + 3 + 5 + 2 = 13

W7=1+2+3+5+8+2=21W_7 = 1 + 2 + 3 + 5 + 8 + 2 = 21

W8=1+2+3+5+8+13+2=34W_8 = 1 + 2 + 3 + 5 + 8 + 13 + 2 = 34

The sequence 1, 2, 3, 5, 8, 13, 21, 34, ... is the Virahānka–Fibonacci sequence.

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