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Question


 Let u n+1 = 2un +1, (n = 0, 1, 2,…) and u0 = 0. Then u10 would be nearest to: (CAT 1993)


Options:
A .   1023
B .   2047
C .   4095
D .   8195
E .   22
Answer: Option A
:
A

Ans: (a)

u n+1 = 2un + 1 (n = 0, 1, 2,…..)

Put n = 0, u1 = 1

n = 1, u2 = 3

n = 2, u3 = 7

n = 3, u4 = 15

n = 4, u5 = 31

Seeing the pattern it is clear that un = 2n – 1

Hence u10 = (2)10 – 1 = 1,023.



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