Computing Numerical Derivatives on a TI-85 or TI-86

Goal: We want to use the numerical derivative function of the calculator.

General method: The calculator has a built-in function, nDer, which computes [f(a+h)-f(a-h)]/(2h) for a small value of h. You can either accept the default value of h or choose your own.

Step by step example: Consider f(x)=x³ – x. We will approximate f Î(2),

• With the cursor in a desired location, enter the CALC menu, and press nDer.
• Complete the resulting expression to nDer(x^3–x, x, 2) and press ENTER.
• Read the results.

Notes:

• The general form is nDer(expression, variable, value). The expression can be a formula or an equation variable such as y1 and may contain more than one variable. The value of variable then determines which is the independant variable.
• The value of h used can be set in the Tolerance menu found in MEMTOL. Set d to the desired value.

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