HP 40gs HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 65
Using functions in the HOME view, view of the Function aplet, they can be reused in
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On the other hand there is a way to further simplify the expression. the result and enclose it with the POLYFORM function as shown right, adding a final ',X' as shown, then highlight it and press . The calculator will expand the brackets and gather terms. Calculator Tip These functions can all be graphed but the speed of graphing is slowed if you don't press first. This is because the composite function is internally re-evaluated for each point graphed. The hp 39gs and hp 40gs are fast enough that the result is still satisfactory but if you have an old 39g or 40g they are slowed to the point of being unusable. Evaluating the function may also hide the domain and for this reason it is sometimes best to leave the evaluation undone. For example, if F1( X ) = X 2 and F 2(X ) = X then F3( X ) = F1(F 2( X )) will show the correct domain of x ≥ 0 for both F2(X) and F3(X) in the NUM view. Pressing will destroy this. Using functions in the HOME view Once functions have been defined in the SYMB view of the Function aplet, they can be reused in the HOME view (and indeed in any other aplet!). For example suppose you needed to find some exact points (x = 0, 1, 2 and 3) for a graph of f ( x) = ( 2x x − 2) when doing a hand sketch of it. Type its definition into the Function aplet SYMB view, switch to the HOME view and then simply type F1(0) and press ENTER. The function will be evaluated for x = 0. Similar results can be obtained for F1(1), F1(2) and F1(3). Notice the error message for x = 2 caused by a divide by zero. A simpler way to get function values is to changing into the NUM view and use its tabular listing. 65