# Contour map of the function showing several level curves

## Homework Statement

ƒ(x,y) = ln(x2+4y2)

## Homework Equations

I'm not really sure but I solved for y

## The Attempt at a Solution

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haruspex
Homework Helper
Gold Member
What do you get for y at x=0 from x2+4y2=1? Where is/are that/those on your diagram?

I'm not sure whether you are supposed to plot curves for equal increments in f, as one would on a cartographic map.

HallsofIvy
Homework Helper
"Level curves" are curves on which the expression has a specific value. I would not solve for y. Instead, I would look at the equation $ln(x^2+ 4y^2)= C$ and recognize that, taking the exponential of both sides, $x^2+ 4y^2= e^C$ which is equivalent to $\frac{x^2}{e^C}+ \frac{y^2}{e^C/4}= 1$. You should immediately see that, for every C, this is an ellipse, centered at the origin, with x intercepts at $\left(-e^{C/2}, 0\right)$ and $\left(e^{C/2}, 0\right)$, y intercepts at $\left(0, -\frac{e^{C/2}}{2}\right)$ and $\left(0, \frac{e^{C/2}}{2}\right)$.

haruspex
Homework Helper
Gold Member
"Level curves" are curves on which the expression has a specific value. I would not solve for y. Instead, I would look at the equation $ln(x^2+ 4y^2)= C$ and recognize that, taking the exponential of both sides, $x^2+ 4y^2= e^C$ which is equivalent to $\frac{x^2}{e^C}+ \frac{y^2}{e^C/4}= 1$. You should immediately see that, for every C, this is an ellipse, centered at the origin, with x intercepts at $\left(-e^{C/2}, 0\right)$ and $\left(e^{C/2}, 0\right)$, y intercepts at $\left(0, -\frac{e^{C/2}}{2}\right)$ and $\left(0, \frac{e^{C/2}}{2}\right)$.
Yes, that was a bit confusing in the OP, but judging from the drawing I would say cosmos42 understood about different values for C.
I was trying to guide cosmos into realising that the curves were centred wrongly.