EXAMPLE 4 Write an equation of a line from a graph Gym Membership The graph models the total cost of joining a gym. Write an equation of the line. Explain.

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EXAMPLE 4 Write an equation of a line from a graph Gym Membership The graph models the total cost of joining a gym. Write an equation of the line. Explain the meaning of the slope and the y -intercept of the line. SOLUTION Find the slope. STEP 1 = 44 m = 363 – – 2

EXAMPLE 4 Write an equation of a line from a graph STEP 2 Find the y -intercept. Use the slope and one of the points on the graph. mx + b y = b 231 = 143 = b Use slope-intercept form. Substitute for x, y, and m. Simplify. STEP 3 Write the equation. Because m = 44 and b = 143, an equation of the line is y = 44x

EXAMPLE 5 Graph a line with equation in standard form Graph 3x + 4y = 12. SOLUTION The equation is in standard form, so you can use the intercepts. STEP 1 Find the intercepts. To find the x -intercept, let y = 0. 3x +4y = 12 3x +4 ( 0 ) = 12 x = 4 To find the y -intercept, let x = 0. 3x +4y = 12 3 ( 0 ) + 4y = 12 y = 3

EXAMPLE 5 Graph a line with equation in standard form STEP 2 Graph the line. The intercepts are (4, 0) and (0, 3). Graph these points, then draw a line through the points.

GUIDED PRACTICE for Examples 4 and 5 5. The equation y = 50x models the total cost of joining a climbing gym. What are the meaning of the slope and the y -intercept of the line? SOLUTION The equation y = 50x models the cost. The slope is monthly fee, $50, and the y - intercept is the initial cost to join the gym, $125.

GUIDED PRACTICE for Examples 4 and 5 SOLUTION 6. 2x – 3y = 6 Graph the equation

GUIDED PRACTICE for Examples 4 and 5 7. y = 4 SOLUTION Graph the equation

GUIDED PRACTICE for Examples 4 and 5 8. SOLUTION x = – 3 Graph the equation