Cubic function : Roots[f] Search
lewws shared this problem 3 years ago
Not a Problem
A student and I were trying to find roots of f(x) = x³ + (k - 6) x² + (2k - 1) x + 30 by varying k on a slider, and using Roots(f).
One of the expected roots is x = -2 since (x+2) is always a factor of f(x) regardless of values of k.
But remaining 2 roots of cubic function depend on values of k.
We were trying to find the repeated root. We set system to 12 decimal places trying to get as close to the repeated root as possible, by varying k and observing the graph
Near to the repeated root we unexpectedly found 4 roots instead of 3. Can we check if there's some algorithm weakness in the system in using Roots to find the roots?
Files: Error in cubic...
You can solve it in CAS. A 3rd degree function with 4roots...???
use root(polynomial) instead roots(function,startx,endx)
the numerical methods are less accuracy
And I could not repeat your issue
Thanks too, mathmagic.
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