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Learn to write equations for lines based on given coordinates, solve for missing coefficients in standard form equations, and practice finding equations of horizontal and vertical lines passing through points.
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Write an equation of the specified line. a. b. Blue line Red line a. 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. 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. EXAMPLE 3 Write an equation of a line SOLUTION
Find the missing coefficient in the equation of the line shown. Write the completed equation. Complete an equation in standard form EXAMPLE 4 EXAMPLE 3 EXAMPLE 4 SOLUTION STEP1 Find the value of A. Substitute the coordinates of the given point for xandyin the equation. Solve forA. Ax + 3y = 2 Write equation. A(–1) + 3(0) = 2 Substitute –1 for x and 0 for y. Simplify. –A = 2 A = –2 Divide by –1.
Complete an equation in standard form EXAMPLE 4 STEP2 Complete the equation. –2x + 3y = 2 Substitute –2 for A.
y=–9, x= –8 ANSWER for Examples 3 and 4 GUIDED PRACTICE Write equations of the horizontal and vertical lines that pass through the given point. 3. (–8, –9)
y=–5, x= 13 ANSWER for Examples 3 and 4 GUIDED PRACTICE Write equations of the horizontal and vertical lines that pass through the given point. 4. (13, –5)
ANSWER 3; –4x + 3y = 7 Complete an equation in standard form EXAMPLE 4 EXAMPLE 3 for Examples 3 and 4 Write an equation of a line GUIDED PRACTICE Find the missing coefficient in the equation of the line that passes through the given point. Write the completed equation. 5. –4x + By = 7, (–1, 1)
ANSWER –7; –7x +y = –3 Complete an equation in standard form EXAMPLE 4 EXAMPLE 3 for Examples 3 and 4 Write an equation of a line GUIDED PRACTICE Find the missing coefficient in the equation of the line that passes through the given point. Write the completed equation. 6.Ax + y = –3, (2, 11)