HP 15c - Manual (Page 20)

20 Section 1: Using _ Effectively
20
The relative field intensity is maximum at an angle of 90° (perpendicular to the tower). To
find the minimum, use angles closer to zero as initial estimates, such as the radian
equivalents of 10° and 60°.
Keystrokes Display
10
´r 0.1745
60 ´r 1.0472 Initial estimates.
´_0 0.4899 Angle giving zero slope.
)) -5.5279 -10 Slope at specified angle.
|(|( 0.4899 Restores the stack.
|d 28.0680 Angle in degrees.
The relative field intensity is most negative at an angle of 28.0680° from vertical.
Using an Approximate Slope
The derivative of a function can also be approximated numerically. If you sample a function
at two points relatively close to x (namely x + Δ and x − Δ), you can use the slope of the
secant as an approximation to the slope at x:

    

2
) ( ) ( x f x f
s