Expressions with a variable
The calculator can handle expressions with a variable x (x button, ‘x’ key). For example, you can type in an expression such as cos( x ) or (x + 1)(x - 1). The main purpose of including support for variable expressions is so that you can create graphs of these expressions. Typically you enter the expression and then use the Graph button to display a graph of the expression you just created.
The calculator supports a limited range of automatic simplifications for expressions you enter. For example, if you enter 4 + x + 2x + xx the calculator (at May 2008) evaluates this as 3x + x2 + 4. (Later versions may improve the order in which the summands are presented.) The calculator does not (at May 2008) support automatic expansion of products, factorisation of sums or combination of trigonometric expressions. These are possible but should not be done automatically because sometimes we wish to expand a product and sometimes to factorise it. There is no uniquely defined simplest form. Similarly, (at May 2008) simplification of rational expressions is limited. For example, (x2 − 1) ÷ (x − 1) is usually simplified to x + 1 but the original expression may be regarded as different because it evaluates to 0 ÷ 0 rather than 2 at x = 1.
At May 2008 variable expressions should be not be regarded as a stable feature of the calculator. Unlike numerical calculations, the variable expressions are not extensively tested. Some changes will also be made. In particular, the order in which terms of a sum or product are displayed needs to be made more consistent.
Last modified: Sat 31 May 2008 01:10 pm