HP 33s - Manual (Page 102)

6–10 Entering and Evaluating Equations
Because many equations have two sides separated by "=", the basic value of an
equation is the difference between the values of the two sides. For this calculation,
"=" in an equation essentially treated as "ಥ". The value is a measure of how well
the equation balances.
The HP 33s has two keys for evaluating equations: ‘ and X . Their
actions differ only in how they evaluate assignment equations:
„ X returns the value of the equation, regardless of the type of equation.
„ ‘ returns the value of the equation — unless it's an assignment–type
equation. For an assignment equation, ‘ returns the value of the right
side only, and also "enters" that value into the variable on the left side — it
stores the value in the variable.
The following table shows the two ways to evaluate equations.
Type of Equation Result for ‘ Result for X
Equality: g(x) = f(x)
Example: x
2
+ y
2
= r
2
g(x) – f(x)
x
2
+ y
2
– r
2
Assignment: y = f(x)
Example: A = 0.5
× b x h
f(x) ¼
0.5 × b × h ¼
y – f(x)
A – 0.5 × b × h
Expression: f(x)
Example: x
3
+ 1
f(x)
x
3
+ 1
¼ Also stores the result in the left–hand variable, A for example.
To evaluate an equation:
1. Display the desired equation. (See "Displaying and Selecting Equations"
above.)
2. Press ‘ or X . The equation prompts for a value for each variable
needed. (If you've changed the number base, it's automatically changed back
to base 10.)
3. For each prompt, enter the desired value:
„ If the displayed value is good, press g .
„ If you want a different value, type the value and press g . (Also see
"Responding to Equation Prompts" later in this chapter.)