You can grab the blue point in the x-y plane and move it around to see how the partial derivatives change.
The red line is the line whose slope computes ; the green line is the line whose slope computes . Both slopes are displayed whenever the corresponding line is.
Use the toggle switches to change visibility:
graphvisible turns the graph of f on and off.
xslicevisible turns the y=constant slice (in which we compute ) on and off.
yslicevisible turns the x=constant slice (in which we compute ) on and off.
xtangentvisible turns the tangent line whose slope is on and off.
ytangentvisible turns the tangent line whose slope is on and off.
Enter your own function in place of the default .