Calculate the Positive Domain: Linear Function Through Point (0,4)

Linear Function Domains with Missing Data

Calculate the positive domain of the function shown in the figure:

(0, 4)(0, 4)(0, 4)xy

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Step-by-step video solution

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00:00 Find the positive domain of the function
00:02 The function is positive when it's above the X-axis
00:05 We don't know the intersection points of the function

Step-by-step written solution

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1

Understand the problem

Calculate the positive domain of the function shown in the figure:

(0, 4)(0, 4)(0, 4)xy

2

Step-by-step solution

The domains of positivity and negativity are determined by the point of intersection of the function with the X-axis, so the Y values are greater or less than 0.

We are given the information of the intersection with the Y-axis, but not of the point of intersection with the X-axis,

Furthermore, there is no data about the function itself or the slope, so we do not have the ability to determine the point of intersection with the X-axis,

And so in the domains of positivity and negativity.

3

Final Answer

Not enough data

Key Points to Remember

Essential concepts to master this topic
  • Domain Rule: Positive domain needs x-intercept to determine where y > 0
  • Key Data: Only y-intercept (0, 4) given; need x-intercept or slope
  • Verification: Check if enough information exists to find x-intercept āœ“

Common Mistakes

Avoid these frequent errors
  • Assuming you can find domains with incomplete information
    Don't try to calculate positive domain using only the y-intercept (0, 4) = wrong assumption! Without knowing where the line crosses the x-axis, you cannot determine where the function is positive or negative. Always identify what information is missing before attempting to solve.

Practice Quiz

Test your knowledge with interactive questions

What is the solution to the following inequality?

\( 10x-4≤-3x-8 \)

FAQ

Everything you need to know about this question

Why can't I use just the point (0, 4) to find the positive domain?

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The point (0, 4) only tells you where the line crosses the y-axis. To find where the function is positive (above the x-axis), you need to know where it crosses the x-axis - that's the boundary between positive and negative regions!

What additional information would I need to solve this?

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You would need either:

  • Another point on the line
  • The slope of the line
  • The x-intercept directly
With any of these, you could find the complete equation and determine the positive domain.

How do I know when a problem doesn't have enough information?

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Ask yourself: "Can I write the complete equation of the line?" For a linear function, you need two pieces of information (like two points, or one point and the slope). If you can't write y=mx+b y = mx + b completely, you likely need more data.

Is 'Not enough data' ever a valid mathematical answer?

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Absolutely! In real mathematics, recognizing when you don't have sufficient information is just as important as solving problems. It shows you understand what's required to find a solution.

What would the positive domain look like if I had the x-intercept?

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If the line crossed the x-axis at point (a, 0), then:

  • For positive slope: positive domain would be x>a x > a
  • For negative slope: positive domain would be x<a x < a

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