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Substitute 3 for x and 4 for y. Simplify. Write original equation. Check whether each ordered pair is a solution of the equation. SOLUTION Which ordered pair is a solution of 3x – y = 7? EXAMPLE 1 Standardized Test Practice (3, 4) A (1, –4) B (5, –3) C (–1, –2) D Test (3, 4) : 3(3) – 4 = ? 7 3x – y =3x – y =7 5 =7

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Simplify. Write original equation. Standardized Test Practice EXAMPLE 1 Test (1, –4): 3x – y =3x – y =7 3(1) – (–4) = ? 7 Substitute 1 for x and –4 for y. So, (3, 4) is not a solution, but (1, – 4) is a solution of 3x – y = 7. ANSWER The correct answer is B. AB DC 7 =7

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GUIDED PRACTICE for Example 1 Tell whether 4, – is a solution of x + 2y = 5. 1 2 not a solutionANSWER

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Solve the equation for y. SOLUTION EXAMPLE 2 Graph an equation Graph the equation –2x + y = –3. –2x + y = –3 y = 2x –3 STEP 1

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Graph an equation EXAMPLE 2 Plot the points. Notice that the points appear to lie on a line. STEP 3 Make a table by choosing a few values for x and finding the values of y. x–2–1012 y–7–5–3–11 STEP 2

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Graph an equation EXAMPLE 2 Connect the points by drawing a line through them. Use arrows to indicate that the graph goes on without end. STEP 4

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Graph (a) y = 2 and (b) x = –1. Graph y = b and x = a EXAMPLE 3 SOLUTION For every value of x, the value of y is 2. The graph of the equation y = 2 is a horizontal line 2 units above the x -axis. a.

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Graph y = b and x = a EXAMPLE 3 For every value of y, the value of x is –1. The graph of the equation x = –1 is a vertical line 1 unit to the left of the y -axis. b.

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GUIDED PRACTICE for Examples 2 and 3 Graph the equation. 2. y + 3x = –2 ANSWER

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GUIDED PRACTICE for Examples 2 and 3 3. y = 2.5 Graph the equation. ANSWER

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GUIDED PRACTICE for Examples 2 and 3 4. x = –4 Graph the equation. ANSWER

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SOLUTION STEP 1 Make a table. x 02468 y43210 EXAMPLE 4 Graph a linear function 1 2 Graph the function y = with domain x 0. – x + 4 Then identify the range of the function.

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STEP 2 STEP 3 Connect the points with a ray because the domain is restricted. STEP 4 Identify the range. From the graph, you can see that all points have a y- coordinate of 4 or less, so the range of the function is y ≤ 4. EXAMPLE 4 Graph a linear function Plot the points.

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GUIDED PRACTICE for Example 4 5. Graph the function y = –3x + 1 with domain x 0. Then identify the range of the function. ANSWER y 1

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SOLUTION RUNNING The distance d (in miles) that a runner travels is given by the function d = 6t where t is the time (in hours) spent running. The runner plans to go for a 1.5 hour run. Graph the function and identify its domain and range. STEP 1 Identify whether the problem specifies the domain or the range. You know the amount of time the runner plans to spend running. Because time is the independent variable, the domain is specified in this problem. The domain of the function is 0 ≤ t ≤ 1.5. Solve a multi-step problem EXAMPLE 5

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Solve a multi-step problem STEP 2 Graph the function. Make a table of values. Then plot and connect the points. t ( hours ) 00.511.5 d ( miles ) 0369 STEP 3 Identify the unspecified domain or range. From the table or graph, you can see that the range of the function is 0 ≤ d ≤ 9.

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SOLUTION EXAMPLE 6 Solve a related problem WHAT IF? Suppose the runner in Example 5 instead plans to run 12 miles. Graph the function and identify its domain and range. STEP 1 Identify whether the problem specifies the domain or the range. You are given the distance that the runner plans to travel. Because distance is the dependent variable, the range is specified in this problem. The range of the function is 0 ≤ d ≤ 12.

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EXAMPLE 6 Solve a related problem STEP 2 Graph the function. To make a table, you can substitute d -values ( be sure to include 0 and 12) into the function d = 6t and solve for t. t ( hours ) 012 d ( miles ) 0612 STEP 3 Identify the unspecified domain or range. From the table or graph, you can see that the domain of the function is 0 ≤ t ≤ 2.

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GUIDED PRACTICE for Examples 5 and 6 GAS COSTS For gas that costs $2 per gallon, the equation C = 2g gives the cost C (in dollars) of pumping g gallons of gas. You plan to pump $10 worth of gas. Graph the function and identify its domain and range. domain: 0 ≤ g ≤ 5, range: 0 ≤ C ≤ 10 6. ANSWER

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