What version of MATLAB are you using? There are no errors when running your code in R2023a.
% 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(f,x) %Solve for the first derivative
%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
%Solve the Equation of the normal line
ynormal = 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")
