Finding the range of values of x where a curve has a negative gradient

Yes.In summary, the conversation discusses solving the inequality 3px^2 - m < 0 and determining where the slope dy/dx is negative. The correct approach is to manipulate the inequality to x^2 < m/3p and then solve for x, resulting in -√(m/3p) < x < √(m/3p). The participant in the conversation may benefit from seeking additional help in understanding mathematical concepts.
  • #1
Natasha1
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9
Homework Statement
Curve C has equation y = px^3 - mx where p and m are positive integers.
Relevant Equations
Find the range of values of x, in terms of p and m, for which the gradient of C is negative.
dy/dx = 3px^2 - m

Where do I go from here please?
 
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  • #2
Is this the right approach?

3px^2 - m < 0

3px^2 < m

x^2 < m/3p

x < Square root of m/3p

Is this correct please?
 
  • #3
Natasha1 said:
Is this the right approach?

3px^2 - m < 0

What do I do here?
This is the right approach. ##p## and ##m## are both positive, so you can work out where the slope ##dy\over dx## is negative.
 
  • #4
BvU said:
This is the right approach. ##p## and ##m## are both positive, so you can work out where the slope ##dy\over dx## is negative.
Am I correct then when I write this?

3px^2 - m < 0

3px^2 < m

x^2 < m/3p

x < Square root of m/3p
 
  • #5
Make a plot for e.g. ##m = 3## and ##p=1## to convince yourself ...
 
  • #6
Natasha1 said:
x^2 < m/3p

x < Square root of m/3p
And check this last step :mad: !
 
  • #7
Are there two solutions plus (Square root of m/3p) and minus (Square root of m/3p)
 
  • #8
Natasha1 said:
Are there two solutions plus (Square root of m/3p) and minus (Square root of m/3p)
You have a range for ##x##. Let's write ##a = m/3p##, so that ##a## is some positive number. We have the equation $$x^2 < a$$ What does that say about ##x##? Try drawing a graph of the function ##x^2##, with the line ##y = a## marked.
 
  • #9
It has two solutions
 
  • #10
Natasha1 said:
It has two solutions
No. You have an inequality. Inequalities typically have a range of solutions.
 
  • #11
What's the solution then, I am stuck.
 
  • #12
Natasha1 said:
What's the solution then, I am stuck.
Let's assume ##a = 1##. What does ##x^2 < 1## tell you?
 
  • #13
That x < + sqrt 1 or x < - sqrt 1
 
  • #14
Natasha1 said:
That x < + sqrt 1 or x < - sqrt 1
Is that what you see on your graph?

E.g. For ##x = -2##, we have ##x < -1## yet ##x^2 = 4 > 1##.
 
  • #15
Never mind, I give up.
 
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  • #16
I need to see the answer to understand where I can't go
 
  • #17
Natasha1 said:
Never mind, I give up.
I recognise your problems with these concepts. You may want to consider a private tutor if grasping the basics of mathematics is important to you. We may not be able to do enough on a forum like this. I can't stand over you and help you draw a graph, for example.
 
  • #18
Natasha1 said:
I need to see the answer to understand where I can't go
Let me give you a basic result of mathematics: $$x^2 < 1$$ is equivalent to $$-1 < x < 1$$
If that's a struggle, then perhaps you need help from someone who has training and knowldege in maths education at this level.
 
  • #19
Where are I going from from here

x^2 < m/3p

x < Square root of m/3p
 
  • #20
Is the answer

- Square root of m/3p < x < + Square root of m/3p
 
  • #21
Natasha1 said:
Is the answer

- Square root of m/3p < x < + Square root of m/3p
Yes.
 
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  • #22
hallelujah
 
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1. What is a negative gradient?

A negative gradient is a measure of the slope or steepness of a curve. It indicates that the curve is decreasing from left to right, meaning that the y-values are getting smaller as the x-values increase.

2. How do you find the range of values of x where a curve has a negative gradient?

To find the range of values of x where a curve has a negative gradient, you can graph the curve and visually identify where the slope is negative. Alternatively, you can take the derivative of the curve and set it equal to a negative value, then solve for x to find the range of values.

3. Can a curve have a negative gradient at only one point?

No, a curve cannot have a negative gradient at only one point. A negative gradient indicates that the curve is decreasing over a range of values, not just at a single point.

4. What does a negative gradient tell us about the behavior of a curve?

A negative gradient tells us that the curve is decreasing, or getting smaller, as the x-values increase. This can indicate a downward trend or a decrease in the rate of change.

5. How does a negative gradient relate to the concavity of a curve?

A negative gradient can indicate a concave down curve, where the slope is decreasing as the x-values increase. However, a negative gradient alone does not necessarily determine the concavity of a curve, as it also depends on the rate at which the slope is decreasing.

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