1. Key in the function you would like to visualize into the input box.[br]2. You can click and drag on the 3D curve to zoom in and out, or rotate the curve to see it from all sides.[br]3. Use the sliders to change the values of a (x-coordinate) and b (y-coordinate) to see point P move on the surface.[br]4. Move the point to change vector u.[br]5. Observe how the value of the directional derivative changes as u changes.[br]6. Refresh the page if anything goes wrong.[br][img]data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxOCIgaGVpZ2h0PSIxOCIgdmlld0JveD0iMCAwIDI0IDI0Ij48cGF0aCBmaWxsPSJub25lIiBkPSJNMCAwaDI0djI0SDB6Ii8+PHBhdGggZD0iTTcgMTRINXY1aDV2LTJIN3YtM3ptLTItNGgyVjdoM1Y1SDV2NXptMTIgN2gtM3YyaDV2LTVoLTJ2M3pNMTQgNXYyaDN2M2gyVjVoLTV6Ii8+PC9zdmc+[/img][br][br]