Variables, functions and the with bar

7.1Store a value in a variable#

A variable name is one or more letters. Store a value with the assign key := (it types :=), or with the store arrow: type the value, press ctrl→:=, then the name. After that the name stands for the value everywhere.

Example 7.1

Store with :=

1. Type a, press assign, type 5, enter. Then type a², enter.

   a:=5enterax²enter

Example 7.2

Store with the arrow

1. Type 3, press ctrl then assign, type c, enter. Then c × 2.

   3ctrl→:=centerc×2enter

Example 7.3

Use two variables

1. Store a and b and add them.

   a:=5enter5ctrl→:=bentera+benter

7.2Define your own function#

Use Define (menu, 1, 1) to make a function you can reuse. Type Define, the function name with its variable in brackets, an equals sign and the rule. The calculator answers Done. You can then call it with numbers or with symbols.

Example 7.4

Define and use f(x)

$$f(x)=x^{2}+1,\quad f(3)=10$$

1. Press menu, 1, 1. Type f(x)=x²+1 and press enter.

   menu11f(x)=x^2▶+1enter

2. Type f(3) and press enter.

   f(3)enter

Example 7.5

Call it with a symbol

1. Define f then type f(a+1).

   define␣f(x)=x^2▶+1enterf(a+1)enter

Example 7.6

A function with two variables

1. Define g(x,y)=xy+1 then find g(2,3).

   define␣g(x,y)=x×y+1enterg(2,3)enter

Example 7.7

Differentiate a defined function

1. Define f(x)=x²+1 then take d(f(x),x).

   define␣f(x)=x^2▶+1enterd(f(x),x)enter

Example 7.8

Solve with a defined function

1. Define f(x)=x²−3x then solve f(x)=4.

   define␣f(x)=x^2▶−3xentersolve(f(x)=4,x)enter

A name of two or more letters followed by a bracket, such as foo(3), is a function call. If no function of that name is defined, it stays as it is. To multiply, type ×: ab·(2). A single letter before a bracket still multiplies: x(x+1) is x·(x+1).

Example 7.9

An undefined function stays as it is

1. Type foo(3).

   foo(3)enter

7.3Delete a variable#

DelVar (menu, 1, 2) removes one variable. Home, 5 removes all of them. The name then goes back to being an ordinary symbol.

Example 7.10

Delete one variable

1. Store a as 3, then DelVar a.

   a:=3enterdelvar␣aenter

7.4Substitute with the with bar#

The with bar (ctrl then ÷) evaluates an expression for particular values without storing them. Write the expression, the bar, then the value as x=3.

Example 7.11

Evaluate at x = 3

$$x^{2}+1\Big|_{x=3}=10$$

1. Type x²+1, ctrl ÷, x = 3.

   x^2▶+1ctrl|÷x=3enter

Example 7.12

Substitute a symbol

1. Type (x+1)², with bar, x = a.

   (x+1)^2▶ctrl|÷x=aenter

Example 7.13

Substitute an exact angle

1. Type sin(x) | x = π/6.

   sin(x)ctrl|÷x=π÷6enter

After the bar you can also give a condition such as x>0. A condition keeps only the solutions of solve( (or the zeros of zeros() that satisfy it. Combine a value and a condition with and.

Example 7.14

Keep only the positive solution

1. Type solve(x²=4, x), the with bar, then x > 0.

   solve(x^2▶=4,x)ctrl|÷xctrl≠≥▸=40enter

Example 7.15

Keep the negative zero

1. Type zeros(x²−4, x) | x < 0.

   zeros(x^2▶−4,x)ctrl|÷xctrl≠≥▸=30enter