Review of Graphing

REVIEW OF GRAPHING

Three ways to graph a line:

1. Plotting points method: Choose any three numbers to be a value for x; then solve for y. This works most effectively when y is isolated, that is when equation is of form:

“ y = ……”

Example: Graph y =2x –1

You may choose any number as a value for x. Then put that value in the equation and solve for y.

__X_____Y_

-1 -3 x = -1: y = 2(-1) – 1 = -2 – 1 = -3

0 -1 x = 0: y = 2(0) – 1 = 0 –1 = -1

2 3 x = 2: y = 2(2) – 1 = 4 – 1 = 3

2. X and y-intercept method: To find x-intercept, let y=0 and solve for x.

To find y-intercept, let x=0 and solve for y.

Plot the intercepts. Draw the line. This method works well when

y is not isolated.

Example: 3x – 2y = 6 .

x-intercept: Let y=0: 3x – 2(0) = 6 3x = 6 x = 2 ;

So, x-intercept is (2, 0)

y-intercept: Let x=0: 3(0) – 2y = 6 -2y=6 y = -3;

So, y-intercept: is (0, -3)

3. Slope-intercept Method: Solve for y first. Then identify the slope and y intercept. Remember that slope = m = from the y-intercept.

Slope-intercept Form of line: y = mx + b where the slope is m and (0,b) is y-intercept.

Example: 3x – 2y = 6

-3x -3x

-2y = -3x + 6

-2 -2

y = ; So: y =

y-intercept: (0,-3) slope = from y-intercept.

Assignment: Page 149: Graph by plotting points: 15, 23, 34;

Graph by slope-intercept method: 21, 25, 31, 35

Graph by x and y intercept method: 27, 37

Graph special lines: x =-2, y =3 (See pg. 157, ex. 5 & 6)