# Algebra Menu - HP -28S Quick Reference

General
This menu contains commands for symbolic manipulation of expressions and
equations. There's also an interactive equation editor available (FORM).
Important: If flag 36 is clear the "numerical" evaluation mode is used. It
evaluates expressions until a numerical result has been found. If an
undefined variable is encountered an error is issued. Thus, in order to to see
the symbolic results in this section flag 36 must be set.
COLCT
Takes an equation or expression and collects similar expressions:
'1+2+LOG(10)' → '4'
'1+X+2'
'X^Z*Y*X^T*Y' → 'X^(T+Z)*Y^2'
'X+X+Y+3*X'
COLCT operates independently on each side of an equation:
'1+2*X=3+4*X' is not simplified to '-2=2*X' or even '-1=X'
EXPAN
Expands an equation or expression:
'A*(B+C)' → 'A*B+A*C'
'(B+C)/A' → 'B/A+C/A'
'A^(B+C)' → 'A^B*A^C'
'X^5'
'(X+Y)^2' → 'X^2+2*X*Y+Y^2'
EXPAN doesn't perform all possible expansions in a single step. It may be
necessary to apply the command repeatedly.
SIZE
Returns the number of objects in an expression or equation. Example:
'XX*LN(Y)=CCC' SIZE returns 6 because there are these objects:
XX, *, LN, Y, =, CCC
FORM
Allows to perform identity manipulations interactively on equations and
expressions.
• When invoked, the expression in stack level 0 is displayed in line 2 (and
line 3 if it doesn't fit in one line) of the LCD display and a number of soft-
key menus are displayed.
• The commands available in the menus depend on the type of sub-
expression that is currently selected by the cursor.
• When done press ON to quit the interactive mode. The expression in level
1 will be replaced by the modified version.
• The FORM editor can be invoked by a program.
COLCT
EXPAN
LEVEL
EXGET
[←]
[→]

→ '3+X'
→ '5*X+Y'
→ 'X*X^4'
Collect similar expressions of the selected sub-expression.
Similar to COLCT above.
Expand products and exponentials of the selected sub-expression.
Similar to EXPAN above.
While this button is held down the level of the currently selected
object or sub-expression is displayed.
Quit the FORM editor and returns:
• In stack level 3: The edited expression.
• In stack level 2: A copy of the currently selected sub-expression.
• In stack level 1: The position index of the sub-expression.
Move cursor left.
Move cursor right.
HP-28S
20  