How do you do a derivative with a certain value?
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My initial equation is f(x) = (3*x^5)-(x^3)+(2*x^2)+4 and when I derive that, I get f'(x)=15*x^4 - 3*x^2 + 4*x. How do I evaluate f'(x) when x = 1.7?
So far I have done this:
clear all, close all
syms x f = (3*x^5)-(x^3)+(2*x^2)+4; diff(f)
This gives me the derivative, but how do I find the value of f'(x) when I have a value for x?
採用された回答
Geoff Hayes
2014 年 10 月 24 日
syms x
f = (3*x^5)-(x^3)+(2*x^2)+4;
df = diff(f);
result = double(subs(df,1.7));
その他の回答 (1 件)
John D'Errico
2014 年 10 月 24 日
help subs
3 件のコメント
John D'Errico
2022 年 12 月 2 日
That was not the question, to solve an ODE, or even work with one. The explicit question was asked as how to evaluate a function that you have differentiated. subs will do that.
But your question is simple to answer. Say your ODE is something easy:
y' = t^2 +2
Now evaluate the right hand side is easy.
syms y(t)
RHS = t^2 + 2;
Now you want to evaluate the right hand side for some value. Say, at t==1. You can use subs here
subs(RHS,t,1)
or you can converty the relation into a MATLAB function, as:
RHSfun = matlabFunction(RHS)
RHSfun(1)
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