Question: Errors when attempting to plot

Greetings,

I have been attempting to plot a couple of functions and I keep getting the same error.  I will copying and paste what I have entered and the error messages

with(plots);

with(VectorCalculus);

sphereplot*(rho = theta, theta = 0 .. 4*Pi, phi = 0 .. (1/2)*Pi);

Error, (in simpl/reloprod) invalid terms in product: (rho = theta)*(theta = 0 .. 4*Pi)

 

with(plots);
with(VectorCalculus);
fieldplot*(<-x, y, cos z>, x = 0 .. 5, y = 0 .. 5, z = 0 .. 2*Pi);
Error, (in simpl/reloprod) invalid terms in product: (x = 0 .. 5)*(y = 0 .. 5)

 

Any assistance would be most appreciated.  Thanks in advance.

 

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