And if we want these expressions to truly be equal, we would have to have them to have the same, if you view them as function definitions, as having the same domain. So this one right over here, this one we already saw is not defined at theta is equal to negative pi over four. And so this one, in order for these to be equivalent, we have to say that this one is also not. And actually other places, but let's just say theta does not equal negative pi over four. And we could think about all of this happening in some type of an open interval around negative pi over four if we wanted to get very precise. But if we, for this particular case, well let's just say everything we're doing is in the open interval. So in open interval, in open interval between theta, or say negative one and one.