Evaluating a Function

1
Evaluating a Function

• Given a function y f(x), we are often
  interested in finding function values for a given
  x. One example would be to find ordered pairs
  for points on the graph of the function.

• To find just one function value, the simplest
  way is to substitute 3 for x in the Home Screen.

2
Evaluating a Function

• If the value of x is more difficult that a
  simple integer, the Store function is very useful.

(1) Enter 3/4 and press STO
(2) Press x and then press ENTER.
Slide 2
3
Evaluating a Function

• The value of .75 or 3/4 is now stored in the
  variable x.

• If a fractional form is desired, press MATH and
  ENTER to select fraction, or Frac.

• The press ENTER again.

• The fractional form can be completed in one
  step.

Slide 3
4
Evaluating a Function

• A third way to evaluate a function is given in
  the next example.

• Enter function f into Y1.

Slide 4
5
Evaluating a Function

• Use QUIT to get to the home screen. Then
  press VARS to get Variables.

• Use the right arrow to highlight Y-VARS at the
  top of the screen, and press ENTER.

• Press ENTER again to paste Y1 into the Home
  Screen.

• Now type (7) and press ENTER. The result is
  f(7), the original problem to be solved.

Slide 5
6
Evaluating a Function

• The evaluation is in approximate decimal form.
  To find the exact value, use MATHFrac.

• Two other ways to evaluate a function are TABLE
  and TRACE, which are described in other modules.
  They will always give the function value in terms
  of a decimal, which may be rounded.

• Thus, one of the most valuable aspects of Y1(
  ) is the ability to find exact function values
  (when x is rational).

Slide 6
7
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