Expressions. The equation does not contain an "=". For example, x3 + 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.