I got a solution using DSolve as :

```
Function[{t}, -((
1. (2. + k (-1. - 2. t) + k^2 (-0.5 + 1. t + 1. t^2)))/k^3) +
E^(-1. k t) C[1]]
```

What does '.' mean and '()'? For example, in the case of '2.+k(-1.-2.t)', what does it mean? How to translate it to normal Math notation?

Pretty simple because the first one is regularly used in languages like C and Java too and the second one actually*is*math-notation. Therefore,

`1.`

just means`1.0`

. In programming languages this is different from a simple`1`

which usually means an integer while`1.0`

means a real number. In*Mathematica*a 1 is a perfect*one*with infinite precision, while`1.0`

has only machine precision.`k(1-t)`

just means`k*(1-t)`

. Parenthesis are used like in normal math too.