Error says: Variable yprime must be of data type symfun. It is currently of type sym. Check where the variable is assigned a value.

% This program computes for the Tangent Line / Normal Line of a curve % about a given point
                   %define x for symbolic processing
syms x 
%IDENTIFY the function f(x)
f(x) = (4*x^2-2*x+1)

%DETERMINE the point of tangency (This will be a random point)
x0=randi([-5,5])
%SOLVE for the Ordinate of the point of tangency
y0=f(x0);  %Evaluate y given value fo x
y=73

%FIND the slope function
yprime= diff(4*x^2-2*x+1)              %Solve for the first derivative

%Determine the slope at the given x0
m=sym(-42)         %Evaluate the slope

%Solve the equation of the tangent line
ytangent = sym(-42*x+1/42)

%Solve the Equation of the normal line
ynormal = sym(((1/42)*x)+215/42)

%DISPLAYING RESULTS
fprintf('The tangent line to f(x)=%s at (%.2f, %.2f) is y = %s \n',string(f(x)),x0,y0, string(ytangent))
fprintf('The normal line to f(x)=%s at (%.2f, %.2f) is y = %s \n',string(f(x)),x0,y0, string(ynormal))

%PLOTTING
g1=ezplot(f,[-15,15]);
set(g1,'color','b')
grid on
hold on
plot(x0,y0,'r*')
text(x0+1,y0,"Point of Tangency")
g2=ezplot(ytangent,[-15,15]);
text(5,5,["y(Tangent)=", string(ytangent)])
pause(1)
set(g2,'color','m')
pause(1)
g3=ezplot(ynormal,[-15,15]);
text(3,3,["y(Normal)=", string(ynormal)])
set(g3,'color','c');
title("Tangent Line and Normal Line")

Variable yprime must be of data type symfun. It is currently of type sym. Check where the variable is assigned a value.
Variable m must be of data type symfun. It is currently of type sym. Check where the variable is assigned a value.
Variable ytangent must be of data type symfun. It is currently of type sym. Check where the variable is assigned a value.
Variable ynormal must be of data type symfun. It is currently of type sym. Check where the variable is assigned a value.

[Dyuman Joshi]

Please copy and paste your full code, not the picture of a part of the code.

And copy paste your full error message, that means all of the red text.

[Dyuman Joshi]

I specifically mentioned not to post a picture and you posted a picture. Smh.

Copy paste the text of the code.

And "And copy paste your full error message, that means all of the red text."

[Girbaud]

There, is that ok?

Answer 1

[Dyuman Joshi]

Looks like you are working on an older version of MATLAB, as your code runs without an error on R2021b.

1 - Use f directly to find the derivative of the function.

2 - Since x is already defined as a symolic variable, you do not need to use sym() for defining ytangent and ynormal.

3 - Additionally, the variable m and the equations ytangent and ynormal are constant, which they shouldn't be, as x0 is not a fixed value/point. Modify the values accordingly.

4 - ezplot is not recommended, use fplot instead.

5 - You might want to rearrange the text on the plot.

syms x 
%IDENTIFY the function f(x)
f(x) = (4*x^2-2*x+1);
%DETERMINE the point of tangency (This will be a random point)
x0=randi([-5,5]);
%SOLVE for the Ordinate of the point of tangency
y0=f(x0);  %Evaluate y given value fo x
y=73;

%FIND the slope function
yprime= diff(f,x)              %Solve for the first derivative

yprime(x) = 

%Determine the slope at the given x0
m=yprime(x0); %sym(-42);         %Evaluate the slope
%Solve the equation of the tangent line
ytangent = -42*x+1/42

ytangent = 

%Solve the Equation of the normal line
ynormal = ((1/42)*x)+215/42

ynormal = 

%DISPLAYING RESULTS
fprintf('The tangent line to f(x)=%s at (%.2f, %.2f) is y = %s \n',string(f(x)),x0,y0, string(ytangent))

The tangent line to f(x)=4*x^2 - 2*x + 1 at (0.00, 1.00) is y = 1/42 - 42*x 

fprintf('The normal line to f(x)=%s at (%.2f, %.2f) is y = %s \n',string(f(x)),x0,y0, string(ynormal))

The normal line to f(x)=4*x^2 - 2*x + 1 at (0.00, 1.00) is y = x/42 + 215/42 

%PLOTTING
%use fplot
g1=fplot(f,[-15,15]);
set(g1,'color','b')
grid on
hold on
plot(x0,y0,'r*')
text(x0+1,y0,"Point of Tangency")
g2=fplot(ytangent,[-15,15]);
text(5,5,["y(Tangent)=", string(ytangent)])
pause(1)
set(g2,'color','m')
pause(1)
g3=fplot(ynormal,[-15,15]);
text(3,3,["y(Normal)=", string(ynormal)])
set(g3,'color','c');
title("Tangent Line and Normal Line")