error in gradient function for partial differential

i want the partial differential of this equation w.r.t X , Y and Z.

31.65951=sqrt((20460991.052399-X)^2+(11012393.207537-Y)^2+(13140061.841029-Z)^2)-sqrt((20462649.31-X)^2+(11012196.356-Y)^2+(13137623.266-Z)^2)

the function send to me to solve this equation was gradient but when trying it an error was happened

Use gradient

 syms X Y Z
 Eq = -31.65951 + sqrt((20460991.052399-X)^2+(11012393.207537-Y)^2+(13140061.841029-Z)^2)-sqrt((20462649.31-  X)^2+(11012196.356-Y)^2+(13137623.266-Z)^2);
 gradient(Eq)

is

error

syms X Y Z Eq = -31.65951 + sqrt((20460991.052399-X)^2+(11012393.207537-Y)^2+(13140061.841029-Z)^2)-sqrt((20462649.31- X)^2+(11012196.356-Y)^2+(13137623.266-Z)^2); gradient(Eq) ??? Error using ==> zeros Trailing string input must be a valid numeric class name.

Error in ==> gradient at 64 g = zeros(size(f),class(f)); % case of singleton dimension