Graphing a Linear Function (Line) There are two formulas to use for graphing a line: Formula 1: y = mx + b m is the slope (how the line “moves”) b is the y intercept (where the line “begins” on the y axis) This formula is used about 2/3 of the time in 9th grade algebra Formula 2: y – y1 = m(x – x1) (x1, y1) is any point that appears on the line This formula is used when the question does not provide a y-intercept (b) value

Graphing a Linear Function (Line) What if we don't know the slope? Find it!! Option 1 – Use the two given points to find the slope using slope formula y2 – y1 x2 – x1 Option 2 – Get the line into y = mx + b format and determine “m”

Graphing a Linear Function (Line) Finding Intercepts: Finding a “y” intercept: Using the given equation, plug in zero for the “x” value and solve for y Finding an “x” intercept: Using the given equation, plug in zero for the “y” value and solve for x

Graphing a Linear Function (Line) Take the equation: y = 2x – 5 b value = -5 start at -5 on the y axis m value = 2 Express as 2/1. slope of 2/1 makes the graph move up 2 to the right 1 Example Question: Is the point (3,1) on the graph of y = 2x – 5?

Graphing a Linear Function (Line) Next Take the equation: y = -4x + 3 Find b and m values Graph the line Decide if the point (-1, 6) is on this graph

Graphing a Linear Function (Line) What to do when the graph doesn’t help you? y = 5x - 2 Find b and m values Graph the line Determine if the point (20, 98) is on this line Now we have to use some algebra (20,98) is a possible point on this line 20 is the x value, 98 is the y value. Plug in to find the b value. If b value matches, then this point is on the line.

Graphing a Linear Function (Line) Example 2: y = -2x + 7 3 Does the point (30, 27) appear on this line?