Math Problem Statement

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Meara drew a graph of a linear function. What is the equation of the line?

Solution

Let's solve this by analyzing the graph.

Step 1: Find the slope of the line

The line passes through the points (0,4)(0, 4) (y-intercept) and (2,2)(2, -2). To find the slope mm, use the slope formula: m=y2y1x2x1m = \frac{y_2 - y_1}{x_2 - x_1} Substitute the points (0,4)(0, 4) and (2,2)(2, -2): m=2420=62=3m = \frac{-2 - 4}{2 - 0} = \frac{-6}{2} = -3

Step 2: Write the equation of the line in slope-intercept form

The slope-intercept form of a line is: y=mx+by = mx + b Where m=3m = -3 and b=4b = 4 (from the y-intercept (0,4)(0, 4)): y=3x+4y = -3x + 4

Step 3: Analyze the given options

Now that we know the slope is 3-3 and the y-intercept is 4, let's check the options:

  1. y=3x+4y = -3x + 4: This is correct. The slope is 3-3 and the y-intercept is 4.
  2. y=3x+4y = 3x + 4: Incorrect, the slope is positive here.
  3. y1=3(x1)y - 1 = -3(x - 1): Let's simplify this. Distribute the 3-3: y1=3x+3y=3x+4y - 1 = -3x + 3 \quad \Rightarrow \quad y = -3x + 4 This matches the correct equation, so this is correct.
  4. y1=3(x1)y - 1 = 3(x - 1): Let's simplify this. Distribute the 3: y1=3x3y=3x2y - 1 = 3x - 3 \quad \Rightarrow \quad y = 3x - 2 This does not match the correct equation, so this is incorrect.
  5. 3x+y=43x + y = 4: Let's rearrange this to the slope-intercept form y=mx+by = mx + b: y=3x+4y = -3x + 4 This matches the correct equation, so this is correct.

Correct answers:

  • y=3x+4y = -3x + 4
  • y1=3(x1)y - 1 = -3(x - 1)
  • 3x+y=43x + y = 4

Would you like further details or clarifications? Here are some related questions:

  1. How can we derive the equation of a line using two points?
  2. What is the general form of a linear equation, and how does it relate to the slope-intercept form?
  3. What happens to the slope when a line is vertical or horizontal?
  4. How can you determine the slope from a graph without explicit points?
  5. How do transformations (translations or scaling) affect the equation of a line?

Tip: Always confirm the slope of a line from its direction on the graph; a downward-sloping line has a negative slope.

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Math Problem Analysis

Mathematical Concepts

Algebra
Linear Equations
Slope-Intercept Form

Formulas

Slope formula: m = (y2 - y1) / (x2 - x1)
Slope-intercept form: y = mx + b

Theorems

Linear equations in slope-intercept form
Graphical representation of linear functions

Suitable Grade Level

Grades 8-10