Relationship of Y^2=f(x) and Y=f(x)

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In summary: If f(a) is positive and a minimum, (f(a))^2 will also be a minimum. In general, if f(a) has a "horizontal tangent" and is an extreme value, then (f(a))2 will have a "vertical tangent" and be an extreme value.In summary, the relationship between y=f(x) and y^2=f(x) is that they are both functions, but y^2=f(x) is not always a function. If f(x) has a maximum or minimum point at (a,b), then y^2=f(x) will have a maximum or minimum point at (a,b^2). However, if f(a) has a "horizontal tangent" and is an extreme value,
  • #1
mune
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hi guys, what is the relationship between y^2 = f(x) and y = f(x)?

thank you.
 
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  • #2
Is that a trick question or is it a very highly theoretical and advanced question? You have indicated a situation in which y^2 = y. Best conclusion is y=1 and f(x)=1, horizontal line, one unit above the x axis.
 
  • #3
symbolipoint said:
Is that a trick question or is it a very highly theoretical and advanced question? You have indicated a situation in which y^2 = y. Best conclusion is y=1 and f(x)=1, horizontal line, one unit above the x axis.

Or y=0...
/*extra characters*/
 
  • #4
let's say we are given a function y=f(x), what is relationship between it and y^2 =f(x)?

for example, if y=f(x) have a maximum point at (a,b), will y^2=f(x) have a maximum point at(a,b) too?

i hope i make my question clear.:smile:
 
  • #5
it is not a trick question, nor a very highly theoretical question.
 
  • #6
mune said:
let's say we are given a function y=f(x), what is relationship between it and y^2 =f(x)?

for example, if y=f(x) have a maximum point at (a,b), will y^2=f(x) have a maximum point at(a,b) too?

i hope i make my question clear.:smile:

Oh, you don't really mean y=f(x), and y2=f(x) do you? I think what you mean to say is if we're given a function f(x), then what is the relation between the function f(x), and the function (f(x))2.

so let's let
y=f(x) and
z=(f(x))2

Obviously z is always positive assuming we are only dealing with real numbers, but to investigate a relation about maxima/minima let's look at y'.

y'=f'(x) and
z'=2f(x)f'(x)

if f(x) has a max/min at the point (a,b) then f'(a)=0
Then y'(a)=0, and I think you can see then that z'(a)=2f(a)f'(a), but f'(a)=0 so z'(a)=0, thus the function z or (f(x))2 will also have a max or min at the point a, however this time it will be at the point (a, b2).

I think it should be fairly easy to show that if f has a min at x=a then so does f2, and the same if f has a max at x=a, but I'm a bit too tired to try a proof of that at the moment.
 
  • #7
No, that's not how I would interpret the question.

Let's clarify by taking f(x)= x. What is the relationship between y= x and y2= x?

Suppose f(x)= x+ 3. What is the relationship between y= x+ 3 and y2= x+ 3?

Frankly, I don't see much relationship. The first is a function and the second, for general f(x), is NOT a function. The first might be a square root of the second (if the first is positive for all x) but that was obvious wasn't it?
 
  • #8
I am quite sure this question is derived from a common one I've seen: Given a sketch of the graph of y=f(x), sketch y^2=f(x) labeling important features. d_leet's post works on that a bit. Also remember to find all points where y= 0 or 1, the graphs intersect there. Between zero and one, the y^2 graph will be slightly above the y graph. Other values, it will be below. You know the y^2 graph is discontinuous at the points where the y graph is negative.
 
  • #9
thank you everyone :smile:
sorry that I didn't explain my question clearly. Anyway, Gib Z and HallsofIvy know what I mean :cool:

but thanks d_leet too, I have learned a way to prove from your post.
 
Last edited:
  • #10
d_leet said:
I think it should be fairly easy to show that if f has a min at x=a then so does f2, and the same if f has a max at x=a, but I'm a bit too tired to try a proof of that at the moment.
That depends on whether f(a) is positive or negative. If f(a) is negative and a minimum, (f(a))^2 may be a maximum (e.g., if f(x) is the cosine function, then f(pi) is a minimum put (f(pi))^2 is a maximum).
 

FAQ: Relationship of Y^2=f(x) and Y=f(x)

What is the difference between Y=f(x) and Y^2=f(x)?

The main difference between these two equations is the presence of the exponent 2 in the latter equation. This changes the relationship between the variables Y and x, as it indicates that Y is a squared function of x. In other words, the value of Y in the second equation is determined by squaring the value of x, whereas in the first equation, Y is solely dependent on the value of x.

How does the graph of Y^2=f(x) compare to the graph of Y=f(x)?

The graph of Y^2=f(x) is a parabola, while the graph of Y=f(x) is a straight line. The parabola is symmetric about the y-axis, and has a minimum or maximum point at the origin, depending on the value of the coefficient of x^2. On the other hand, the line in Y=f(x) has a constant slope and intersects the y-axis at the y-intercept.

Can Y^2=f(x) and Y=f(x) have the same solutions?

Yes, it is possible for these two equations to have the same solutions. This occurs when the value of x is 0, as both equations will result in Y=0. However, in all other cases, the solutions will be different, as the parabola and line have different shapes and properties.

What is the relationship between the roots of Y^2=f(x) and Y=f(x)?

The roots, or solutions, of Y^2=f(x) are related to the roots of Y=f(x) in that they are the same values, but squared. For example, if the root of Y=f(x) is x=2, then the root of Y^2=f(x) is x=4. This is because squaring a number yields the same result as multiplying that number by itself.

How can Y^2=f(x) be used in real-life applications?

The equation Y^2=f(x) can be used in various real-life applications, such as in physics and engineering, to model and analyze relationships between variables. For example, in the equation for the kinetic energy of an object, KE=1/2mv^2, the squared term represents the relationship between velocity (v) and kinetic energy (KE). This relationship can be expressed as Y^2=f(x), where Y represents KE and x represents v.

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