An Iterated Fraction

Problem

Let f(x)=x+ax+1f(x) = \dfrac{x + a}{x + 1} for x>0x > 0, and suppose the tangent line to y=f(x)y = f(x) at (1,f(1))(1, f(1)) has yy-intercept 112\dfrac{11}{2}.

1. Find aa. 2. Discuss the monotonicity of g(x)=x⋅f2(x)g(x) = x \cdot f^2(x). 3. Let a1=1a_1 = 1 and an+1=f(an)a_{n+1} = f(a_n) for n∈N∗n \in \mathbb{N}^*. Prove that

2n−2∣2ln⁡an−ln⁡7∣<1.2^{n-2}\left|2\ln a_n - \ln 7\right| < 1.

Answer

Solution

Difficulty8/10
Topicsfunctions, calculus, Monotonicity, Recursion, sequences, Logarithms

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