the elements of my symbolic matrix are functions

this is my code

syms l xita(t)

r0=[l/4*cosd(xita);l/4*sind(xita)];
dfr0=diff(r0,t)

dfr0(t) = 

drf0 is a symbolic matrix, i want to refer to an element in the matrix, but drf0(1) or drf0(2) is t = 1/2, so how can i get one element in the matrix, thank you!

Answer 1

[binbin cao]

I have found a solution to the problem. formula