### Home > CALC > Chapter 3 > Lesson 3.4.4 > Problem3-187

3-187.

HANAH STRIKES AGAIN!
To calculate the slope of a line tangent to $f(x)$ at $x = a$, most graphing calculators use Hanah's method from problem 3-35, formally called the Symmetric Difference Quotient, shown below.

$\lim\limits_ { h \rightarrow 0 } \frac { f ( x + h ) - f ( x - h ) } { 2 h }$

1. Use the symmetric difference quotient to find $f^\prime(x)$ if $f(x) = 3x-2$.

$f'(x)=\lim\limits_{h\rightarrow 0}\frac{(3(x+h)-2)-(3(x-h)-2)}{2h}$

Expand the numerator.
Combine like terms.
Factor out an $h$.
Cancel out the $h$.
Evaluate the limit $h→0$.... this is $f^\prime(x)$.

2. Use this symmetric difference in your graphing calculator to graph $f^\prime(x)$ for $f(x) =\operatorname{sin }x$ for $h = 0.001$.

$f'(x)\approx \lim\limits_{h\rightarrow 0.001}=\frac{(3(x+0.001)-2)-(3(x-0.001)-2)}{2(0.001)}=\underline{ \ \ \ \ \ \ \ \ \ \ \ }$
Graph that on your calculator. Also sketch the derivative function you found in part (a). The sketches should look a lot alike.