HP 40gs HP 39gs_40gs_Mastering The Graphing Calculator_English_E_F2224-90010.p - Page 300

Finding critical points and graphing a polynomial

Page 300 highlights

Finding critical points and graphing a polynomial For the function f (x) = x3 − 4x2 + x + 6 ... (i) find the intercepts. (ii) find the turning points. (iii) draw a sketch graph showing this information. (iv) find the area under the curve between the two turning points. Step 1. Enter the function into the SYMB view of the Function aplet, so it is available for plotting. Step 2. Use the POLYROOT function to find the roots. This function is in the MATH menu in the Polynom. group. See page 204 for more information. The results show that the x intercepts are (−1, 0), (2, 0) and (3, 0) . The y intercept is found by evaluating F1(0) in the HOME view giving the point (0,6). Step 3. Switching to the PLOT view via VIEWS - Decimal, you will find that the function does not display as well as it could. Since it is the y axis that is not displaying enough, we will use the 'Y-Zoom Out' option in the menu after first setting the Zoom factors to 2 rather than 4 (which is too drastic). The Zoom factors setting is also found in the menu. Now use the pop-up menu to find the Extremum (both left and right). The snapshot right shows the left-hand turning point of (0.131,6.065). 300

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Finding critical points and graphing a polynomial
For the function
f x
2
+
+
6
()
=
x
3
4
x
x
(i)
find the intercepts.
(ii)
find the turning points.
(iii)
draw a sketch graph showing this information.
(iv)
find the area under the curve between the two turning points.
Step 1.
Enter the function into the
SYMB
view of the Function aplet, so
it is available for plotting.
Step 2.
Use the
POLYROOT
function to find the roots. This function is
in the
MATH
menu in the
Polynom.
group. See page 204 for
more information.
The results show that the x intercepts are
( 1,0),(2,0)
and
(3,0)
. The y intercept is found by evaluating
F1(0)
in the
HOME
view giving the point (0,6).
Step 3.
Switching to the
PLOT
view via
VIEWS
-
Decimal
, you will
find that the function does not display as well as it could.
Since it is the y axis that is not displaying enough, we will use
the ‘
Y-Zoom Out
’ option in the
menu after first setting
the
Zoom factors
to 2 rather than 4 (which is too drastic).
The
Zoom factors
setting is also found in the
menu.
pop-up menu to find the
Extremum
(both
left and right). The snapshot right shows the left-hand turning
point of (0.131,6.065).
Now use the
300