When is a Linear Equation Not a Function?

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A linear equation is of the general form y = mx + b. This is a function if f(x) gives a unique value.

If y = f(x) = k, where k is a constant, for any value of x, y = f(x) has the same value. As a result y = k is a linear equation but not a function.

A linear equation does not represent a function when there is more than one value of x that gives the same value of y.

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