Linear Graphs

We often draw graphs with linear scales for x and y that depict a linear relationship.

Parts of a Graph

• Legend: shows what each line and symbol represents
• Symbols (square and diamond): show the location of the data points
• Line: helps visualize the overall shape of the points
• Ticks and Tick Labels: show the linear scale of the x and y axes
• Color: helps reader distinguish

Drawing a Graph

When you draw a graph, think about what you are communicating to your audience.

• What is the story you are trying to tell?
• What is the range of data on the x and y axes?
• Where should you place ticks and tick labels
• Draw out axes, ticks, labels
• Draw the data points on the graph
• Decide if shapes, color, and size would help you
• Draw the trendline
• Draw any annotations

Spreadsheet Graphing

• Find menu item for insert graph
• We usually want a “scatter” plot
• Choose the data for the x and y
• Set colors and sizes and labels to annotate graph

Creating Linear Data

y = mx + b

• Create a column of x values
• Create a cell for the slope
• Create a cell for the y-intercept
• Use relative and absolute references to make the formula y=mx+b in a column for the y-values

Regression

If you have data and you want the computer to find the best slope, you use a technique called regression.

• In most graphs, there is an option to show the trendline and display the equation of the trendline
• You can also show R^2 which is a measure of how closely the data matches the trendline
• There are also functions for the slope and intercept that you can use without a graph