Mathematics 9709 · AS & A Level · Numerical solution of equations

Numerical solution of equations — practice question

The equation $\cot\left(\frac{1}{2}x\right) = 3x$ has a single root in the interval $0 < x < \pi$, and this root is called $\alpha$.
(a)[2]

Show, through calculation, that $\alpha$ lies between $0.5$ and $1$.

(b)[2]

Show that, should a sequence of positive values produced by the iterative formula $x_{n+1} = \frac{1}{3}\left(x_n + 4\tan^{-1}\left(\frac{1}{3x_n}\right)\right)$ converge, it converges to $\alpha$.

(c)[3]

Use this iterative formula to find $\alpha$ correct to $2$ decimal places. Record the outcome of each iteration to $4$ decimal places.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: Calculate the values of a suitable expression at $x=0.5$ and at $x=1$.

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