Summary 221 Section 2.3 Equations of a Line Key Concepts Standard Form: (A and B are not both zero) Ax By C Horizontal line: Vertical line: Slope-intercept form: Point-slope formula: y k y mx b y y1 m1x x12 x k Slope-intercept form is used to identify the slope and y-intercept of a line when the equation is given. Slope-intercept form can also be used to graph a line. The point-slope formula can be used to construct an equation of a line, given a point and a slope. Examples Example 1 Find the slope and y-intercept. Then graph the equation. Solve for y. Slope-intercept form 2y 7x 4 0, 2 72 The slope is the y-intercept is ( ). 54321 1 2 3 4 5 (0, 2) 5 4 3 2 2 3 4 Example 2 Find an equation of the line passing through the point (2, 3) and having slope m4. Using the point-slope formula gives y y1 m1x x12 y 132 41x 22 y 3 4x 8 y 4x 5 Right 2 Up 7 Start here y x 5 ; y 7 2 x 2 7x 2y 4
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