Domain of a function

What is the domain of f(x) = x² + 2x + 1 ?

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Domain is the set of x-values, or the "input"
Range is the set of y-values, or the "output"

As you'll notice in the graph, 

The domain {set of x-values} consists of
all real numbers.

The range {set of y-values} consists of 
all real numbers greater than or equal to 0.

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