plotted 3 graph, only 2 shown up

v = 5 - x - y;
a = 8 - 2*x - y;
plot(v, '-g'); hold on;
plot(a, '-b'); hold on;

w = 8 - x - 2*y;
plot(w, '-r'); hold on;

here's the result:

What's wrong?

Answer 1

[Star Strider]

Nothing is wrong.

Note that if the ‘x’ and ‘y’ vectors have the same values, ‘a’ and ‘w’ are the same, so ‘w’ over-plots ‘a’.

EDIT — (20:30)

What are the values of ‘x’ and ‘y’?

[Joshua Sinamo]

I think it supposed to look like this in regards to the line

Edit 2: u, a, v, x, y suppose to be positive

[Star Strider]

What are the numeric values of ‘x’ and ‘y’ ?

[Joshua Sinamo]

X >= 0 and y >= 0

[Star Strider]

So if any numbers will do, try this:

x = [1 9];
y = [7 2];
v = 5 - x - y;
a = 8 - 2*x - y;
plot(v, '-g'); hold on;
plot(a, '-b'); hold on;

w = 8 - x - 2*y;
plot(w, '-r'); hold on;

That produces 3 distinct lines.

—————

EDIT — (20:32)

I still have no idea what you are doing or what you (and probably your instructor) want.

However, if you arbitrarily choose any two values for ‘x’, you can calculate the corresponding values for ‘y’, and that defines the relevant lines in the plot you posted.

x =  [0; 8]
v = 5 - x - y                       % Equation
vy = 5 - x                          % Find Corresponding ‘y’ Values
a = 8 - 2*x - y
ay = 8 - 2*x 
w = 8 - x - 2*y
wy = (8 - x)/2

You can then substitute in the corresponding values for both ‘x’ and ‘y’ to replicate the curves in your plot.

Since I still have no idea what you are doing or what Question you are asking, I will delete my Answer (and all the subsequent Comments to it) in a few days if this is not what you want.

Answer 2

[madhan ravi]

Try:

    syms x y

    v = 5 - x - y;
    a = 8 - 2*x - y;
    w = 8 - x - 2*y;
    h=ezplot(v);
    h.Color='g'
    hold on;
    h1=ezplot(a)
    h1.Color='b'
    h2=ezplot(w)
    h2.Color='r'
    grid on
    axis equal

[Joshua Sinamo]

Do you have any alternatives without using the symbolic math toolbox?

[madhan ravi]

x = linspace(0,1000,1000); %x greater than zero so is y
y = x;
v = 5 - x - y;
    a = 8 - 2*x - y;
    w = 8 - x - 2*y;

      plot(v,'r')
      hold on
      plot(a,'g')
      hold on
       plot(w,'-ob')

[madhan ravi]

a and w are overwritten each other but how does symbolic toolbox evaluate the values ? +1 for your question

[Joshua Sinamo]

The code still not showing the graph that I wanted. I saw that there are 2 functions which overlap with the other one according to matlab graph, but those functions are supposed to look like this on the graph. I graphed this on desmos

Those two functions are : 8 - x - 2y and 8 - 2x - y; or am I wrong on this?

[madhan ravi]

as I said symbolic toolbox evaluates it correctly but why doesn't the numerical solution correlate? it's a mystery to me now