Rationality of `tan 1^o`.

 Is `tan 1^o` a rational number?

Using the sum formula for tangent,

`tan （a +b） = (tan a + tan b)/(1- tan a tan b)`

we see that if `tan 1^o` is a rational number, then so is `tan 2^o`, and so is `tan n^o` for any integer `n`. But `tan 60^o = sqrt(3)`, which is irrational, a contradiction. 

Hence `tan 1^o` is not rational!