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The solutions of

x2+2x−6=0

are α and β, where β>α.

A researcher is comparing the efficacy of root-finding algorithms, and wants to compare two different methods for approximating β using a starting value of x=1.6

  1. Use the quadratic formula to find the exact value of β

  2. Using the iterative formula

    xn+1=6−2xn,x0=1.6

    find two further approximations for β.

  3. Use the Newton-Raphson method to find two further approximations, again starting from x=1.6

  4. By considering appropriate percentage errors, compare the efficacy of the two methods.


Let P be the percentage error when using the iterative method in (b), and Q be the percentage error when using the Newton-Raphson method in (c).

Give the value of PQ, correct to 1 significant figure.