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Intervals:

The intervals on a graph that are going up when reading the graph from left to right are increasing. The ball is pink over the increasing intervals on the graph. The intervals on the graph that are going down when reading the graph from left to right are decreasing.The ball is blue over the decreasing intervals on the graph.

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Writing up intervals

Once you've identified the interval, you need the x axis value on the left for the first value. On that side, head straight up or down to the X AXIS value. If it runs off towards negative infinity on the left side of the interval, use - ∞. Then identify where it ends on the right side, and head straight up or down to the X AXIS value. If it runs off towards infinity on the right side, use ∞. Put both values in parentheses seperated by a comma. If there is more than one interval, put a U in between them.

Decreasing interval is (- ∞, -2). Increasing interval is (-2, ∞). Decreasing interval:(-2,2). Increasing intervals:(- ∞, -2) U (2, ∞).
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Intervals using Ti-84:

If you have an equation, use the calculator to get the turning points. You'll use the x coordinate values from the turning points to write up the intervals. On the calculator, the CALC menu will call them maximums or minimums. Instructions here.