According to the Cambridge Dictionary, a broken line graph is "a graph that shows information as dots that are connected by straight lines." These graphs do not necessarily form an overall straight line. Each data point is often a vertex where the line makes a change in direction.
Broken line graphs are one way to show information. Users of these graphs often choose this method of representing changes in data over time, such as changes in stock market prices throughout a day or changes in daily temperatures. The lines allow users to interpolate unknown data values between two dots representing known values.
In such graphs, convention dictates one independent variable horizontally on the xaxis and the dependant variable vertically on the yaxis. Broken line graphs are also useful in presenting data collected over time when a third variable exists. An example includes a broken line graph showing monthly temperature averages for two different locations. The preparer uses different colors for the lines to represent each city, allowing graph users to easily compare trends that exist. While line graphs are simple to construct using graph paper and a ruler, a spreadsheet such as Excel allows users to construct professionallooking representations of data they collect.
They are used for when each data group contains two different sets of frequency data. A double bar graph is used to compare both between and within data groups
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used to show how something changes over a period of time, Broken Line Graph is used to show how something changes over a period of time, for example the sales of CD's over a 20 year
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The slope is defined as rise/run or y/x. To solve it, you use 2 coordinates from that graph and use the formula m=X1/X2  Y1/Y2.
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They both show info.
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