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APPENDIX 3           CUSTOM FUNCTIONS HELP FILE                      395



               dZydx2
                Returns the second derivative of a function y  = F(x), represented by a formula  in a cell,
                at a specified value of  x.  Returns #DIV/O!  error value if x = 0,  in which case use the
                optional argument scale-factor.

                Syntax
                d 2ydx2 (expression, variable, scale-factor)
                expression    reference to a cell containing a formula (the function F(x)to be
                              differentiated)
                variable      cell reference corresponding to the independent variable x  in the
                              function F(x)
                scale-factor   optional argument to be used when x is zero

                Remarks
                   The argument expression can be either a reference to a cell that contains a formula,
                   or a name.
                   The argument variab/e can be either a reference to a cell,  or a name.
                   Use the optional argument scale-factor  to specify a suitable value of x to be used to
                   calculate ~x. For example, if the function requires values of x in the range -1 x  lo5
                   to 1 x  lo5, use 1E-5 for scale-factor.
                   The optional argument scale-factor  can be either a number or a formula,  or a
                   reference to a cell that contains a number or formula, or a name.
                   The workbook can be set to either RlC1- or Al-style.
                   Errors (difference between returned value and correct value,  when the latter can be
                   calculated using a calculus formula)  are typically of the order of   to lo-'.


                Limitations
                   None of the precedent cells of the argument expression may contain references to
                   the argument reference.
                   The function cannot handle implicit references; that is, a name or range reference
                   cannot be used for a range of values.

                Example
                If cell C2 contains the formula  =SIN(62)  and cell 62 contains the value 1, the formula
                =d2ydx2(C2,62)  returns the value -0.841470981782962,  The correct value is cos
                (l+n/2)  = -0.841470984807897  (3.6  x   O/O  error).
                See Also
                dydx
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