HP 40gs HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 298
Appendix A: Some Worked Examples, Finding the intercepts of a quadratic
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42 APPENDIX A: SOME WORKED EXAMPLES The examples which follow are intended to illustrate the ways in which the calculator can be used to help solve some typical problems. In some cases more than one method is shown. In some cases the method is chosen more to illustrate the capabilities of the calculator than because it is necessarily the most efficient method. Sometimes these problems are quoted elsewhere in the book and repeated here for convenience. Finding the intercepts of a quadratic Find the x intercepts of the quadratic equation g(x) = 2x2 + 2x −1 Method 1 - Using the QUAD function in HOME. This method is shown right, using the key in the bottom view. This is probably not a method that one would use in general but it has the slight advantage that the answer is given in the same form that you would see it if you used the Quadratic formula. Just the result, edit and square the decimal part to find the value of the discriminant if you need the result in surd format. The 'S1' is the calculator's version of the ± sign. Just the result and remove the S1 to obtain the positive solution, replacing the + with a - to obtain the other. This method is only of use if the question said "Show working" because it doesn't give the answer directly. Method 2 - Using the Function aplet. Shown right. Enter the function into the SYMB view, use the VIEWS key and choose 'Decimal'. If the axes don't suit, then use the options. Now use the option of Root to find the two roots. One result is shown. This is clearly the best method and has the advantage that you can see the graph clearly. Note: Using the Root method does not depend on the graph being on the screen. The algorithm will still find roots even if they are not currently visible. 298