Mathematica Tutor

Part 3: Variables

1. Enter
   x=3
   y=2
   
   
2. Enter
   2*x+y
   
   
3. The result of the preceding step follows from the fact that the variable x has been assigned the value 3 and the variable y has been assigned the value 2. Check this by entering
   x
   y
   
   
4. Enter the following line. Note that it ends with a semicolon.
   z=5;
   Now, without using a semicolon, enter
   z
   Entering a line with a semicolon has the same long-term effect as entering it without a semicolon, but nothing is displayed afterwards.
   
   
5. Use pencil and paper to decide what number xy² + 3z represents, and then check your answer by entering
   x*y^2+3*z
   Use your mouse to return to the expression just entered, replace the 3 by 4, and press SHIFT-RETURN.
   
   
6. Suppose we want to remove the identification of x with 3. Enter
   x=.
   Check this by entering
   x
   Note: You may also remove an identification with the Clear command. Using this method, you would enter
   Clear[x]
   Now remove the identifications of y with 2 and z with 5. Check by entering
   x*y*z
   You should see
   
   x y z

   as the output.

Note: Mathematica allows variable names with more than one letter. This is sometimes the cause of some confusion, because Mathematica also lets you leave out the * for multiplication.

• x y with a space means the same as x*y .
  
  
• xy without a space means a variable with the name xy .

To avoid confusion, we will always include the * character to indicate multiplication.

7. Mathematica distinguishes between = and ==. The single equals sign is used for definitions. The double equals sign is used to enter equations. Check this by entering
   Solve[s^2 - s - 1 == 0, s]
   (Here the s after the comma in the command tells Mathematica what to solve for.)
   
   
8. Enter
   2+3
   and then
   % + 5
   The percent sign has the value of the last quantity calculated. Check this by entering
   x*y
   and then
   % + z