1. SOLUTION EXAMPLE 3 Write an equation of a line Write an equation of the specified line. The y- coordinate of the given point on the blue line is –4. This means that all points on the line have a y- coordinate of –4. An equation of the line is y = –4. a.a. The x- coordinate of the given point on the red line is 4. This means that all points on the line have an x- coordinate of 4. An equation of the line is x = 4. b.b. Blue line a.a. Red line b.b.

2. Simplify. Find the value of A. Substitute the coordinates of the given point for x and y in the equation. Solve for A. STEP 1 SOLUTION EXAMPLE 4 Find the missing coefficient in the equation of the line shown. Write the completed equation. Ax + 3y = 2 A(–1) + 3(0) = 2 –A = 2 A = –2 Write equation. Substitute –1 for x and 0 for y. Divide by –1. EXAMPLE 3EXAMPLE 4 Complete an equation in standard form

3. EXAMPLE 4 Complete an equation in standard form Complete the equation. –2x + 3y = 2 Substitute – 2 for A. STEP 2

4. Write equations of the horizontal and vertical lines that pass through the given point. GUIDED PRACTICE for Examples 3 and 4 3. (–8, –9) y = –9, x = –8 ANSWER

5. GUIDED PRACTICE for Examples 3 and 4 4. (13, –5) y = –5, x = 13 ANSWER Write equations of the horizontal and vertical lines that pass through the given point.

6. EXAMPLE 4 Complete an equation in standard form Find the missing coefficient in the equation of the line that passes through the given point. Write the completed equation. EXAMPLE 3 Write an equation of a line GUIDED PRACTICE for Examples 3 and 4 5. –4x + By = 7, (–1, 1) ANSWER 3; –4x + 3y = 7

7. EXAMPLE 4 Complete an equation in standard form EXAMPLE 3 Write an equation of a line GUIDED PRACTICE for Examples 3 and 4 6. Ax + y = –3, (2, 11) Find the missing coefficient in the equation of the line that passes through the given point. Write the completed equation. ANSWER –7; –7x +y = –3