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Published byWinifred Gregory Modified over 6 years ago

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Quick graphs using Intercepts 4.3 Objective 1 – Find the intercepts of the graph of a linear equation Objective 2 – Use intercepts to make a quick graph of a linear equation

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x y An x-intercept is the x-coordinate of a point where a graph crosses the x-axis. A y-intercept is the y-coordinate of a point where a graph crosses the y-axis. The x-intercept is the value of x when y = 0 The y-intercept is the value of y when x = 0

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EXAMPLE 1 Finding Intercepts Find the x-intercept and the y-intercept of the graph of the equation 2x + 3y = 6 To find the x-intercept of 2x + 3y = 6, let y = 0 2x + 3y = 6Write the original equation 2x + 3(0) = 6Substitute 0 for y x = 3 The x-intercept is 3. The line crosses the x-axis at the point (3, 0) To find the y-intercept of 2x + 3y = 6, let x = 0 2x + 3y = 6Write the original equation 2(0) + 3y = 6Substitute 0 for x y = 2 The y-intercept is 2. The line crosses the y-axis at the point (0, 2) 2x = 6 Solve for x 3y = 6 Solve for y

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You try it Find the x-intercept and the y-intercept of the graph of the equation 3y = -6x + 3 To find the y-intercept of 3y = -6x + 3, let x = 0 3y = -6x + 3 Write the original equation 3y = -6(0) + 3 Substitute 0 for x y = 1 The y-intercept is 1. The line crosses the y-axis at the point (0, 1) To find the x-intercept of 3y = -6x + 3, let y = 0 3y = -6x + 3 Write the original equation 3(0) = -6x + 3 Substitute 0 for y x = ½ The x-intercept is ½. The line crosses the x-axis at the point (1/2, 0) 6x = 3 Solve for x 3y = 3 Solve for y 0 = -6x + 3 Add 6x to both sides +6x

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EXAMPLE 2 Making a Quick Graph Graph the equation 3x – 2y = 6 x y Find the intercepts 3x – 2y = 6 Write the original equation 3x – 2(0) = 6 Substitute 0 for y x = 2Solve for x The x-intercept is 2 3x – 2y = 6 Write the original equation 3(0) – 2y = 6 Substitute 0 for x y = -3Solve for y The y-intercept is -3 Draw a coordinate plane that includes the points (2, 0) and (0, -3). Plot the points (2, 0) and (0, -3). and draw a line through them. (2, 0) (0, -3) 3x – 2y = 6

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