Define variables.

The empty white box in the middle of the worksheet is an input cell. Click in the input cell and type in the following text:

R = 250e3	# ohms
C = 4e-6	# Farads
tau = R * C
tau

To evaluate the cell, press Shift-Enter or click the evaluate link, which is found just below the bottom-left corner of the input cell. As soon as the code executes, an empty input cell appears on the screen below the previous cell. The screen will look like this:

Perform a calculation.

You can also insert an empty input cell by moving the cursor into the blank space above or below an existing cell. When a thin, solid bar appears in the blank space, click to insert a new input cell. Enter the following code in the next input cell:

v0 = 20.0    # Volts
t = 1.0      # seconds
v0 * exp(-t...