HP (Hewlett-Packard) F2215AA#ABA ユーザーズマニュアル

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Expressions. The equation does not contain an "=". For example, x
3
 + 1 
is an expression.
When you're calculating with an equation, you might use any type of equation — 
although the type can affect how it's evaluated. When you're solving a problem for 
an unknown variable, you'll probably use an equality or assignment. When you're 
integrating a function, you'll probably use an expression.
Evaluating Equations
One of the most useful characteristics of equations is their ability to be evaluated — 
to generate numeric values. This is what enables you to calculate a result from an 
equation. (It also enables you to solve and integrate equations, as described in 
chapters 7 and 8).
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 is essentially treated as "–". The value is a measure of how well 
the equation balances.
The HP 35s has two keys for evaluating equations: 
 and 
.  Their 
actions differ only in how they evaluate assignment equations:
 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.