How to get the positive root of the cubic a*x^3+3*b*x^2+3*c*x+d=0

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How to get the positive root of the cubic a*x^3+3*b*x^2+3*c*x+d=0 where a=1,c=b+2, d=-3 and b=.1:.1:2.
If rr is the root, find rr/(rr+1) for each b.

Accepted Answer

Kye Taylor
Kye Taylor on 17 Apr 2013
Edited: Kye Taylor on 17 Apr 2013
You can try
b = .1:.1:2;
a = 1;
c = b+2;
d = -3;
posR = zeros(1,length(b));
for i = 1:length(b)
r = roots([a,3*b(i),3*c(i),d]);
posR(i) = r(r>0); % only one real root for the values you specified
posR(i) = posR(i)/(posR(i)+1);
end

More Answers (2)

rania saidi
rania saidi on 14 Mar 2021
Résolution équation ax3+bx2+cx+d=0 MATLAB

rania saidi
rania saidi on 14 Mar 2021
Résolution équation a*x^3+b*x^2+c*x+d=0 a=6 ; b=1 ; c=-4; d=1 dans matlab

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