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