Let the temperature T in a body be independent of z so that it is given by a scalar function T = T(x, t). Identify the isotherms T(x, y) = const. Sketch some of them.

Sketch or graph isotherms of the following fields and describe what they look like.

(a) x² - 4x - y²             (b) x²y - y³/3

(c) cos x sinh y          (d) sin x sinh y

(e) e^x sin y                 (f) e^2x cos 2y

(g) x⁴ - 6x²y² + y⁴     (h) x² - 2x - y²