# i need to plot this function and determine the exact valuse of the derrivative at x=1

2 views (last 30 days)
adriana resendez on 13 Feb 2015
Commented: adriana resendez on 13 Feb 2015
F(x)= 2x^3-3x+4 for the interval [-2,2]
Amit on 13 Feb 2015
what is the question? Are you asking how to use plot function?
adriana resendez on 13 Feb 2015
yes

Eduardo Márquez on 13 Feb 2015
Edited: Eduardo Márquez on 13 Feb 2015
Check help symbolic, if blue letter show it's oknd run:
% help symbolic
clear all; clc; close all;
syms fx x % Declare syms functions f(x) and x
fx = 2*(x^3) - 3*x + 4; % Funtion f(x)
Dfx = diff(fx,x); % f'(x)
xx=-2:.1:2;
subv = subs(fx,x,1); % Evalue f(x), x=1;
dfx1 = double(subv) % Back to double the answer
ez1=ezplot(fx,xx);
hold on
ez2=plot(1,dfx1,'ro'); % Show the point
##### 3 CommentsShow 1 older commentHide 1 older comment
Eduardo Márquez on 13 Feb 2015
Edited: Eduardo Márquez on 13 Feb 2015
Check and modific the line
subv = subs(fx,x,1); % Evalue f(x), x=1;
by
subv = subs(Dfx,x,1); % Evalue f'(x), x=1;
Sorry
Final code is:
% help symbolic
clear all; clc; close all;
syms fx x
fx = 2*(x^3) - 3*x + 4;
Dfx = diff(fx,x);
xx=-2:.1:2;
subv = subs(fx,x,1);
dfx1 = double(subv)
ez1=ezplot(fx,xx);
hold on
ez2=ezplot(Dfx,xx);
set(ez2,'color',[1 0 0])
ez3=plot(1,dfx1,'ro');
adriana resendez on 13 Feb 2015
mkay