What is tan(x-pi)?

We'll have to use the following identity to compute tan(x
- `pi` ).

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

We'll replace a and b by x and `pi`, such
as:

`tan (x - pi )` = `(tan x - tan pi)/(1 + tan x*tan
pi)`

But `tan pi = sin pi/cos pi = 0/-1 =
0`

`tan (x - pi) = (tan x - 0)/(1 + tan
x*0)`

`tan(x - pi) = tan
x`

Therefore, the value of tangent of the
difference `x - pi` remains the same as the value of the tangent of the angle
x.