An interval is a section or portion of either the vertical or horizontal axis. In this course we will use inequalities to describe intervals, although you may have already experienced other notations such as brackets \([a,b]\) or parentheses \((a,b)\text{.}\)

In the exercise below, practice writing inequalities to describe the shaded intervals on each number line.

Information for how to input interval or inequality notation from your keyboard.

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Exercise1.2.1

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Subsection1.2.2Function Characteristics

A function can be *positive* or *negative*.

On a graph, if the output values of a function are above the horizontal axis, we say the function is *positive*. If the output values of a function are below the horizontal axis, we say the function is *negative*.. If the output value is zero, touching the horizontal axis, we say the function is *zero* (neither positive nor negative).

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Exercise1.2.2Positive or Negative

A function can be *increasing* or *decreasing*.

If the output values of the function *increase* as the input increases, we say the function is *increasing*. If the output values of the function *decrease* as the input increases, we say the function is *decreasing*.

Reading the graph from left-to-right, a function is increasing if its graph goes up and decreasing if its graph goes down.

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Exercise1.2.3Increasing or Decreasing

A function can be *concave up* or *concave down*.

If a function curves upward (like a cup that holds water), we say the function is *concave up*. If a function curves downward (like an inverted cup that does not hold water), we say the function is *concave down*.

Another way to think about concavity is to imagine a straight metal wire. While one end of the wire is fixed, if the other end is pushed up the wire is now concave up. If that other end is pushed down the wire is concave down.

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Exercise1.2.4Concave Up or Concave Down

Now let's put all these function characteristics on the same graph. Using 24 hour time with midnight at \(t = 0\text{,}\) the graph in the next exercise shows the temperature variation in a small northern town during one day.

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Exercise1.2.5

Finally, let's put these characteristics into context. In the next problem, you will describe the characteristics of various functions given by verbal descriptions.

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Exercise1.2.6