| 1 | initial version |
The problem is that calling v3(k*pi/2) will try to call each component of v3 with that positional argument, but the last component of v3 is 1/6, so calling it with a positional argument is not supported. You can call it with a keyword argument instead, by using v3(t=k*pi/2). To be even more explicit, you can write v3.subs(t=k*pi/2).
Similarly for a3. Then your code works:

| 2 | No.2 Revision |
The problem is that calling v3(k*pi/2) will try to call each component of v3 with that positional argument, but the last component of v3 is 1/6, so calling it with a positional argument is not supported. You can call it with a keyword argument instead, by using v3(t=k*pi/2). To be even more explicit, you can write v3.subs(t=k*pi/2). Similarly for a3.
Similarly for Or, what you probably meant to do: make a3v3. Then callable too:
v3 = diff(r3,t)
a3 = diff(v3,t)
With both approaches, your code works:

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