The first step in simplifying a rational expression is to it's numerator and denominator.
a. multiply
b. subtract
c. factor
d. divide

The answer is C i.e. Factor

Step-by-step explanation:

A rational expression is an expression containing fractions in which both numerator and denominator are polynomials

So to simplify a rational expression we have to make the factor of it

For example:

When we simplify it

we make factors of and

=

=

which is a simplified expression

A graphing calculator or graphing software is required to plot these functions.
Graphing the functions manually requires creating a table as shown below.

For the sake of brevity, only a few points are shown in the table. 
For the plot shown below, the spacing in t/π is 0.05 instead of 0.5.

   t/π             x(t)          y(t)
 ------     -----------  -----------
      0              0              1
    0.5    0.0040   0.9626
    1.0     0.0307   0.8567
    1.5     0.0970   0.7006
    2.0    0.2101     0.5199
    2.5    0.3646   0.3426
    3.0    0.5439   0.1928
    3.5    0.7230   0.0858
    4.0    0.8739   0.0252