Rearranging functions/inverse relationships

In summary, the conversation is about how to rearrange the equation z = f(x,y) to find r(x,y) when x = r cos(theta) and y = r sin(theta). The solution involves finding r in terms of x and y, using a trig identity, and ultimately equating x^2 + y^2 = 1 to find r(x,y).
  • #1
adron
5
0

Homework Statement


Say z = f(x,y) where x = r cos(theta) and y = r sin(theta), how would I go about rearranging this to find r(x,y)?


Homework Equations





The Attempt at a Solution


I thought maybe I should find r in terms of x and y and then equate them, but I don't think that's right.. a point in the right direction would be much appreciated.
 
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  • #2
What's x^2+y^2? Find a trig identity to use on that expression in terms of r and theta.
 
  • #3
Ok, so now I have
r = (x^2 + y^2)/sqrt(cos^2 theta + sin^2 theta)

since x^2 + y^2 = 1.

Is that correct? And is that the same as r(x,y)?
 
  • #4
adron said:
Ok, so now I have
r = (x^2 + y^2)/sqrt(cos^2 theta + sin^2 theta)

since x^2 + y^2 = 1.

Is that correct? And is that the same as r(x,y)?

x^2+y^2=r^2*(sin(theta)^2+cos(theta)^2). Isn't that what you mean??
 
  • #5
x^2 + y^2 = 1 doesn't it?
so then (r cos(theta))^2 + (r sin(theta))^2 = 1 = x^2 + y^2
And then I just rearranged them to find r in terms of x,y.
 

Related to Rearranging functions/inverse relationships

What is a function?

A function is a mathematical relationship between a set of inputs and a set of outputs, where each input has exactly one output. Functions are often represented by equations or graphs.

What does it mean to rearrange a function?

Rearranging a function means to manipulate the equation or graph of the function in order to solve for a different variable or to change the format of the relationship between the inputs and outputs.

What is an inverse relationship?

An inverse relationship is a type of function where the inputs and outputs are switched. In other words, the output becomes the input and the input becomes the output. This is also known as an inverse function.

How do you find the inverse of a function?

To find the inverse of a function, you can use algebraic methods such as solving for the input variable in terms of the output variable. You can also use graphical methods by reflecting the original function over the line y=x.

Why is understanding inverse relationships important in science?

Inverse relationships are commonly found in the natural world and understanding them allows scientists to make predictions and draw conclusions about the relationships between different variables. It also helps with problem-solving and finding solutions in various scientific fields such as physics, chemistry, and biology.

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