Sketching for isotherms $T(x, y) = \text{ const}$ Hi I came across this question 

Let the temperature $$T(x,y) = 4x^2+16y^2$$ in a body be independent of $z$, identify the isotherms $T(x, y) = \text{ const}$. Sketch it.

I do not understand the question. What type of equation(s) do I have to sketch?

For several different values of $C$, you should draw lines containing all the points $(x, y)$ that solve $4x^2 + 16y^2 = C$, and you should also describe what the isotherms look like for a general value of $C$. For example, if $C = 16$, then the graph you would draw is $\frac{x^2}{4} + y^2 = 1$ (this is an ellipse with center at the origin, semi-major axis $2$, and semi-minor axis $1$).
