Appendix
A-5: Evaluation
Example A-5.1
Evaluate x2+3 x−5 for
x=7
x=a2−1−a2
Solution
Maple Solution - Interactive
Part (a)
Control-drag (or type) the given expression.
Context Panel: Evaluate at a Point≻7
x2+3 x−5→evaluate at point65
Part (b)
Expression palette: Evaluation template
Context Panel: Evaluate and Display Inline
x2+3 x−5x=a|f(x)x=a2−1−a2 = a2−1−a22+3a2−31−a2−5
If the evaluation is at a value that is easily typed into a dialog box, the Context Panel options are convenient. However, if the value is more cumbersome, then the evaluation template can be the more convenient tool.
Maple Solution - Coded
Assign the given expression to q1.
q1≔x2+3 x−5
Use the eval command for immediate evaluation.
q2≔evalq1,x=7
Use the Eval command for delayed evaluation. Apply the value command to execute the evaluation.
q3≔Evalq1,x=a2−1−a2
valueq3
The older subs command, which makes a literal replacement, is not equivalent to the eval command because it does not evaluate after making the replacement. For example, using subs to set x=0 in x/sinx returns 0 because Maple sees 0/sin0 and does not evaluate the denominator to zero. The eval command evaluates the denominator to zero, and Maple issues a division-by-zero error, as it should. In general, the eval command should be used for making "substitutions" into expressions; subs is used for strictly literal replacements.
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