1 | initial version |

This happens because of the way python handles variables, assignment, and references. Try the following:

```
sage: var("x,a")
(x, a)
sage: x = cos(a)
sage: a = 1/4
sage: print x
cos(a)
sage: print(a)
1/4
```

In this code, `a`

at first refers to a symbolic variable, then the name `a`

is reassigned to the number 1/4. When x gets printed you still see the symbolic variable there whose name is `a`

.

To get a value for `a`

substituted into `x, y, z`

try using the .subs method:

```
sage: var('a')
a
sage: x = cos(a)
sage: x.subs(a=1/4)
cos(1/4)
```

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