Texas Instruments TI-83 PLUS - Manual (Page 73)

TI-83 Plus Math, Angle, and Test Operations 70
nDeriv(
nDeriv( (numerical derivative) returns an approximate derivative of
expression with respect to variable , given the value at which to calculate the
derivative and H (if not specified, the default is 1 âL 3). nDeriv( is valid only
for real numbers.
nDeriv( expression , variable , value [ , H ] )
nDeriv( uses the symmetric difference quotient method, which
approximates the numerical derivative value as the slope of the secant
line through these points.
ε
ε ε
2
) ( ( ) (
) ( '
− − +
=
x f x f
x f
As H becomes smaller, the approximation usually becomes more
accurate.
You can use nDeriv( once in expression . Because of the method used to
calculate nDeriv( , the TI-83 Plus can return a false derivative value at a
nondifferentiable point.