how to write a function for quadratic equation

I wrote this into matlab but it doesn't work, can someone explain why?

function [x1,x2] = QuadraticEquation (a,b,c)
d=b^2-4*a*c;
if d>=0
disp ('two roots exist')
x1=(-b-sqrt(d))/2*a
x2=(-b+sqrt(d))/2*a
plot(x1,0,'rx',x2,0,'rx')
hold on
x=-10:10
y=a*x.^2+b*x+c
plot(x,y)
hold off
else
disp ('no real roots’)
end

[Matt J]

First explain to us why you think it doesn't work.

[Alisha Mistry]

It keeps saying the variables a,b,c aren't defined but i put them into a script as a function so why does it still say that message?

[Image Analyst]

You need to pass in something. You can't just click the green Run triangle on the toolbar. See Matt J's Answer below.

Answer 1

[Matt J]

[x1,x2] = QuadraticEquation (1,-2,0)

function [x1,x2] = QuadraticEquation (a,b,c)
    d=b^2-4*a*c;
    if d>=0
    disp ('real roots exist')
    x1=(-b-sqrt(d))/(2*a); %<---------- brackets in denominator
    x2=(-b+sqrt(d))/(2*a); %<---------- brackets in denominator
    plot(x1,0,'rx',x2,0,'rx')
    hold on
    fplot(@(x) a*x.^2+b*x+c) %<---------- fplot is more convenient here
    hold off
    else
    disp ('no real roots') %<---------- missing quote
    [x1,x2]=deal([])   %<---------- missing default assignment
    end
end

[Grady]

This code will not work for me I am using 2024a.

[Steven Lord]

What does "will not work" mean in this context?

• Do you receive warning and/or error messages? If so the full and exact text of those messages (all the text displayed in orange and/or red in the Command Window) may be useful in determining what's going on and how to avoid the warning and/or error.
• Does it do something different than what you expected? If so, what did it do and what did you expect it to do?
• Did MATLAB crash? If so please send the crash log file (with a description of what you were running or doing in MATLAB when the crash occured) to Technical Support so we can investigate.

Show us how you tried to use this code as well.