## Thomas' Calculus 13th Edition

$b$
In the graph $b$ of 3D surface it has been seen that in the surface there is a wave that goes from one side to the other. Therefore, this tells us that the graph of 2D level curves has lines curved more when it travels along the axes . The level curves has less curved when it moves furthest away from them which are in the middle of the quadrants as shown in the graph $b$.