# Find the domain and range of two functions

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State the domain and range for each of the following functions

(a) f(x) = ln(1 + x squared)

(b) f(x) = 1 / (over) x-1 + 1 / (over) x-2

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This solution shows how to find the domain and range of two nonlinear functions, with explanatory pictures.

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If you have a function f(x) and you want to know its domain and range, there are two questions you need to ask:

1. For which values of x does f(x) exist? (domain)

2. What values of f(x) are possible? (range)

We usually answer question 1 by thinking of what values of x wouldn't allow us to find f(x). Finding the range is a little more complicated.

(a) f(x) = ln(1 + x^2)

1. Domain: What problems can we have evaluating the ln function? We know that it doesn't exist at 0 or at negative numbers. But will (1+x^2) ever be 0 or negative? Well look at x2. It's never any smaller than 0:

so when we add 1, we'll never get anything smaller than 1:

So we'll always be taking the ln of something 1 or bigger. That means ln(1+x^2) exists for all real x, since we don't need to worry about those negative numbers. The domain is all real numbers.

2. Range: let's see, what values can ln take on? All real values, ...

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