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  • Perplex
    IB Math AAHL
    /
    Proof and Reasoning
    /

    Problem Bank

    [Maximum mark: 21]

    Consider the real numbers ​p​ and ​q​ such that ​−1<p,q<1.

    1. Find the range of possible values of

      1. ​arctanp​

        [2]

        To earn a crown, get your answer ready before you reveal the options!

      2. ​arctanp−arctanq​

        [2]
    2. Prove that ​arctanp−arctanq≡arctan(1+pqp−q​).

      [4]

    Let ​a∈Z,a≥1.

    1. Show that ​0<arctan(a+1)−arctan(a−1)<2π​.

      [4]
    2. Using the identity in (b), verify that ​arctan(a+1)−arctan(a−1)=arctan(a22​)​

      [2]
    3. Using the results from (b) and (d), and the method of mathematical induction, prove that

      ​
      r=1∑n​arctan(r22​)=arctan(n)+arctan(n+1)−4π​
      ​

      for all ​n∈N.

      [7]

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