Answer:
(-infinity, +infinity)
Step by-step explanation:
Here we're working with a log function. For any base, the domain is x > 0. If we focus on the argument of this particular log function, (1+x^2), we see that log (1+x^2) is defined for all x. No problem if x = 0 here; the "1" in (1+x^2) takes care of that. No problem if x grows very large; the log function can handle it.
Thus, we conclude that the domain of this function is
(-infinity, +infinity). Never mind that this function appears as part of an equation; our job is to find the domain of the logarithmic expression on the left side of the "=" sign.