MDFP Introduction to Mathematics Linear Functions 3 ways to graph a straight line

Table of values Slope-intercept Intercept-intercept You NEED to know all three!

Plotting Linear Graphs If the rule for a relation between two variables is given, then the graph of the relation can be drawn by constructing a table of values.rule table To plot a straight line graph we need to find the coordinates of at least two points that fit the rule.coordinates Example 1 Plot the graph of y = 2x + 1.

Table of values This is the slowest method BUT it always works Example y = 2x + 1 Make a table of values Choose at least 3 values for x Substitute your x values in to equation to find y values You now have 3 sets of coordinates (-1, -1) (0, 1) (1, 3) Plot the points and join to form your line x y

(1,3) (0,1) (-1,-1)

Slope-intercept Faster method and NOT difficult Example The line intercepts the y axis at (0, -2) Plot this point The slope is From point of y intercept plot the next point. ie move +3 in y direction and +7 in x direction

+7 +3

Intercept-intercept This is the easiest and quickest method There is NO need to change the equation in to the form y = mx + c At intercept points we have (0, …..) and (….., 0) i.e. either x = 0 or y = 0

Example 2x + 3y = 12 Let x = 0 then 3y = 12 y = 4 We have the coordinate point (0, 4) Let y = 0 then 2x = 12 x = 6 We have the coordinate point (6, 0)

(0,4) (6,0)

1.9 Sketch the graph of each line