Analyzing the Linearity of y = -2x: Increasing or Decreasing?

Linear Functions with Negative Slopes

Given the following function:

y=2x y=-2x

Is the function increasing or decreasing?

–4–4–4–2–2–2222444666–2–2–2222444000

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Is the function increasing or decreasing?
00:03 The function equation according to the given data
00:08 The function's slope is negative according to the given data
00:11 When the function's slope is negative, the function is decreasing
00:14 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Given the following function:

y=2x y=-2x

Is the function increasing or decreasing?

–4–4–4–2–2–2222444666–2–2–2222444000

2

Step-by-step solution

To determine if the function y=2x y = -2x is increasing or decreasing, we need to consider its slope.

The function y=2x y = -2x is a linear function of the form y=mx+b y = mx + b , where:

  • m=2 m = -2 (the slope)
  • b=0 b = 0 (the y-intercept)

The slope m m is the rate of change of the function. For linear functions:

  • If the slope m>0 m > 0 , the function is increasing.
  • If the slope m<0 m < 0 , the function is decreasing.

In this case, the slope m=2 m = -2 is negative (m<0 m < 0 ). This indicates that as x x increases, y y decreases, meaning the function is decreasing.

Therefore, the function y=2x y = -2x is decreasing.

3

Final Answer

Decreasing

Key Points to Remember

Essential concepts to master this topic
  • Rule: Negative slope means function decreases as x increases
  • Technique: For y=2x y = -2x , slope m = -2 < 0
  • Check: Pick two points: when x = 1, y = -2; when x = 2, y = -4 ✓

Common Mistakes

Avoid these frequent errors
  • Confusing slope sign with function behavior
    Don't think negative slope means the line goes down on the graph = wrong interpretation! The slope tells you the rate of change, not the visual direction. Always remember: negative slope means as x increases, y decreases.

Practice Quiz

Test your knowledge with interactive questions

Is the function in the graph decreasing? yx

FAQ

Everything you need to know about this question

Why does a negative slope mean the function is decreasing?

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The slope tells us the rate of change. When the slope is negative, like -2, it means for every 1 unit increase in x, y decreases by 2 units. So as we move right, we go down!

How can I tell if a function is increasing or decreasing just by looking at it?

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Look at the coefficient of x (the slope). If it's positive, the function increases. If it's negative, the function decreases. For y=2x y = -2x , the coefficient is -2, so it's decreasing.

What does the -2 in the equation actually mean?

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The -2 is the slope of the line. It means for every 1 step right (positive x direction), you take 2 steps down (negative y direction). That's why the line slopes downward!

Can I check this by plugging in numbers?

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Absolutely! Try x = 0: y = -2(0) = 0. Try x = 1: y = -2(1) = -2. Try x = 2: y = -2(2) = -4. Notice how as x gets bigger, y gets smaller? That's decreasing!

Is y = -2x the same as 2x + y = 0?

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Yes! These are the same equation written differently. Both represent the same decreasing line with slope -2. You can rearrange one form to get the other.

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