9709 P3 - Nov 2005 - Q4
1817
The equation \(x^3 - x - 3 = 0\) has one real root, \(\alpha\).
(i) Show that \(\alpha\) lies between 1 and 2.
Two iterative formulae derived from this equation are as follows:
\(x_{n+1} = x_n^3 - 3, \quad (A)\)
\(x_{n+1} = (x_n + 3)^{\frac{1}{3}}, \quad (B)\)
Each formula is used with initial value \(x_1 = 1.5\).
(ii) Show that one of these formulae produces a sequence which fails to converge, and use the other formula to calculate \(\alpha\) correct to 2 decimal places. Give the result of each iteration to 4 decimal places.
