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

Numerical solution of equations — practice question

(i)[2]

Verify by calculation that the cubic equation $x^3 - 2x^2 + 5x - 3 = 0$ has a root between $x = 0.7$ and $x = 0.8$.

(ii)[2]

Show that this root also obeys an equation of the form $x = \frac{ax^2 + 3}{x^2 + b}$, with the values of $a$ and $b$ still to be found.

(iii)[3]

With these values of $a$ and $b$, apply the iterative formula $x_{n+1} = \frac{ax_n^2 + 3}{x_n^2 + b}$ to find the root correct to $2$ decimal places. Show the result 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: Examine the sign of $x^3-2x^2+5x-3$ at $x=0.7$ and $x=0.8$

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