Unrecognized function or variable 'a'.

My teacher assigned me a task to find the first and second derivative of f(x,y,z) and given f(x,y,z) = (a*x+b*y+c*z)*asin(x*y*z). Here is my work:

syms x y z;

f = (a*x + b*y + c*z) * (asin(x*y*z));

disp('Dao ham rieng cap 1 cua f theo x:')

diff(f,x);

Why do I get this error? Can someone explain please

Answer 1

[Dyuman Joshi]

You get an error because you have undefined variables in your code, that are a, b and c.

If they have any numeric value, then assign the values. Otherwise, define them as symbolic variables

syms x y z a b c
f = (a*x + b*y + c*z) * (asin(x*y*z));
disp('Dao ham rieng cap 1 cua f theo x:')

Dao ham rieng cap 1 cua f theo x:

diff(f,x)

ans = 

Answer 2

[Selena Mastrodonato]

Hi Dao,

you have to add a, b and c in syms command:

syms x y z a b c
f = (a*x + b*y + c*z) * (asin(x*y*z));
disp('Dao ham rieng cap 1 cua f theo x:')

Dao ham rieng cap 1 cua f theo x:

diff(f,x)

ans =