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Which math sentence can be used to determine if the triangle is a right triangle?

The given dot plot represents the average daily temperatures, in degrees fahrenheit, recorded in a town during the first 15 days of september. if the dot plot is converted to a box plot, the first quartile would be drawn at __ , and the third quartile would be drawn at link to the chart is here

Use sigma notation to represent the following series for 9 terms.