Section 3.5 Point-Slope Formula 265 Skill Practice 7. Write an equation for the vertical line that passes through the point (7, 2). Answer 7. x 7 Although standard form and slope-intercept form can be used to express an equation of a line, often the slope-intercept form is used to give a unique representation of the line. For example, the following linear equations are all written in standard form, yet they each define the same line. 2x 5y 10 4x 10y 20 6x 15y 30 2 5 The line can be written uniquely in slope-intercept form as: Although it is important to understand and apply slope-intercept form and the point-slope formula, they are not necessarily applicable to all problems, particularly when dealing with a horizontal or vertical line. Writing an Equation of a Line 12, 42 Find an equation of the line passing through the point and parallel to the x-axis. Solution: Because the line is parallel to the x-axis, the line must be horizontal. Recall that all horizontal lines can be written in the form y k, where k is a constant. A quick sketch can help find the value of the constant. See Figure 3-34. Example 5 y 25 x 2. x y 2 5 y 1 543 1 2 3 4 5 21 1 2 3 4 5 x 4 3 2 (2, 4) y 4 Figure 3-34 Because the line must pass through a point whose y-coordinate is then For additional exercises, see Classroom Activity 3.5A in the the equation of the line must be y 4. 4, Section 3.5 Practice Exercises Study Skills Exercise Student’s Resource Manual at www.mhhe.com/moh. Prepare a one-page summary sheet with the most important information that you need for the test. On the day of the test, look at this sheet several times to refresh your memory instead of trying to memorize new information. Writing Translating Expression Geometry Scientific Calculator Video Classroom Example: p. 268, Exercise 48
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