Question

Suppose p" must approximate p with relative error at most 10-3 . Find the largest interval in which p* must lie for each value of p.

Answer 1

`[p-|p|*10^(-3) \, , \, p+|p|* 10^-3]`

Explanation

The relative error is the absolute error divided by the absolute value of p. for an approximation p*, the relative error is

r = |p*-p|/|p|

we want r to be at most 10⁻³, thus

|p*-p|/|p| ≤ 10⁻³

|p*-p| ≤ |p|* 10⁻³

therefore, p*-p should lie in the interval [ - |p| * 10⁻³ , |p| * 10⁻³ ], and as a consecuence, p* should be in the interval [p - |p| * 10⁻³ , p + |p| * 10⁻³ ]