# Evaluating Equations - HP 35s User Manual

Scientific calculator.

Expressions. The equation does not contain an "=". For example, x
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:
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,
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.
6-10
Entering and Evaluating Equations
and
returns the value of the right
3
+ 1
. Their  