how to write a function for quadratic equation?

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I wrote this into matlab but it doesn't work where express x1, x2, it express only one sol in d>=0 but ploting is work in d>=0. and it's error in d<0
why it doen't work and how to fix it?
function [x1,x2] = f(a,b,c)
if a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
end
d=b^2-4*a*c;
if (d>=0)&&(~(a==0))
x1=((-b-sqrt(d))/(2*a));
x2=((-b+sqrt(d))/(2*a));
plot(x1,0,'rx',x2,0,'rx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
elseif a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
else
[x1 x2]=[]
end
  4 Comments
jun
jun on 25 Sep 2022
i want d<0 => empty value return
but a=0&d<0 => x1=x2=-c/b return that i want

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Accepted Answer

VBBV
VBBV on 25 Sep 2022
if (d>=0) & (~(a==0))
use binary operator &
  11 Comments
Dyuman Joshi
Dyuman Joshi on 26 Sep 2022
Let me highlight it. See the green parts, both are same.
I would suggest you to remove the top one and edit last else as
elseif d<0
function [x1,x2] = f(a,b,c)
%{
if a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
end
%}
d=b^2-4*a*c
if (d>=0)&&(~(a==0))
x1=((-b-sqrt(d))/(2*a));
x2=((-b+sqrt(d))/(2*a));
plot(x1,0,'rx',x2,0,'rx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
%{
elseif a==0
x1=-c/b;
x2=-c/b;
plot(x1,0,'gx',x2,0,'gx')
hold on
fplot(@(x) a*x.^2+b*x+c)
hold off
%}
else
x1 = [];
x2 = [];
end
end

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