2025 VJC Promo Q8

2025 VJC Promo Q8

Junior College 1
8 marks
  1. A sequence \(x_r\) for \(r = 0, 1, 2, 3, \ldots\) is such that \(x_r = x_{r-1} + \ln(r + 1) + 3, \qquad \text{for all}\hspace{0.5em} r \geq 1.\) It is given that \(x_0 = 6\).
    1. Find the exact values of \(x_1, x_2\) and \(x_3\), leaving your answers in the form \(A + \ln(B)\), where \(A\) and \(B\) are constants to be determined.[2]
    2. Find \(x_n\) in terms of \(n\).[2]
  2. Arithmetic progression \(U\) has first term \(a\) and common difference \(u\). Another arithmetic progression \(V\) has first term \(b\) and common difference \(v\). It is given that
    • \(a\) is a non-zero integer,
    • the product of the first 3 terms of \(U\) is 0,
    • the sum of the first terms and common differences of both progressions is \(-11\),
    • the \(12^{\text{th}}\) term of \(U\) is three times of the \(10^{\text{th}}\) term of \(V\),
    • the sum of first 50 even-numbered terms of \(V\) is 5800.
    Write down and solve equations to find the values of \(a, u, b\) and \(v\).[4]

Solution:

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Answer:\(x_n=3n+6+\ln((n+1)!)\); \(a=-9,u=4.5,b=-9,v=2.5\)

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