1 | initial version |

To define the variable `k`

, you can write:

```
sage: var('k')
k
```

Concerning problem 5, Sage does not answer the right result:

```
sage: solve(limit(cos(x), x=pi/2, dir='-') == limit(sin(x+k), x=pi/2 , dir='+'), k)
[k == 1/2*pi]
```

Indeed, `1/2*pi`

is one of the solutions, but the solutions are all numbers of the form `1/2*pi+n*pi`

(where `n`

is an integer). So, you have to be careful with symbolic computations.

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