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```									Quadratic Functions…
and their
applications!
For a typical basketball shot, the ball’s
height (in feet) will be a function of time
in flight (in seconds), modeled by an
equation such as h = -16t2 +40 t +6.
a) What is the maximum height of the ball?

b) When will the shot reach the height of
c) When will the ball hit the floor, if it
a) What is the maximum
height of the ball?
 Put it in your calculator!
 Use your zooms and change   your
window until you see the maximum.
 Find the maximum!

height of the ball is 31 feet!
b) When will the shot reach the
height of the basket? (10 feet)
 Key    words to highlight:
When (so we are looking for our x)
Height of the basket (10 feet)

 Put   10 in for y2 and find the…
INTERSECTION!

c) When will the ball hit the floor, if
 What   do we put in for y2?
y2 = 0
 Now    find the intersection!

Answer: The ball will hit the
floor after 2.64 seconds!
Miss Bakewell (who loves to swim!) is putting in a
swimming pool next to her house. She wants to put a nice,
rectangular privacy fence around it, but she can only afford to pay
for 50 feet of fencing. If she does not need a fence on the part
adjacent to her house, what are the dimensions of the fence with
the largest area she could have for her pool?
Help me get the most
My house!
space for my money!
2x + y = 50
y = 50 - 2x
Area = x 50 – 2x
y
A = x(50 – 2x)
A = 50x – 2x2
Now graph it!
x ft.

x ft.               y ft.
My pool will
go here!      My future
fence!
Maximum Area                Put it in your
calculator and
350
300                                     find the
250                                     what???
MAXIMUM
Area

200
Do we need the
150
x value or the y
100
value?
50
0                                      x value!
x = 12.5 ft.
0      10            20   30
thus y = 50 – 2(12.5)
Length                     y = 25
Dimensions of the
Fence:
25 ft x 12.5 ft
A farmer wants to build two rectangular
pens of the same size next to a river so
they are separated by one fence. If she
has 240 meters of fencing and does not
fence the side next to the river, what are
the dimensions of the largest area
enclosed? What is the largest area?
Step 1: Draw a figure!

xm      xm      xm

ym
Step 2: Set up your equations!
Perimeter equation        3x + y = 240
Area equation                A = xy
Solve for y!               y = 240 – 3x
Substitute y into the
area equation             A = x(240 – 3x)
Distribute the x.          A = 240x – 3x2
Now what type of function do we have????

So
graph it!
Step 3: Graph it!
Remember: There are two questions in the problem.
1. What are the dimensions of the largest area
enclosed?
2. What is the largest area?
So when we graph and find the maximum, are we looking for the x or y
for number 1?
x!
So when we graph and find the maximum, are we looking for the x or y
for number 2?
y!
The Chesapeake Bay
Average Monthly Temperatures of
the Chesapeake Bay
Month   Jan   Feb Mar    Apr May Jun    Jul   Aug Sep   Oct   Nov Dec
Temp    31    34    44   54   64   72   76    75   68   57    47   36

1. Turn on your STAT PLOT and Diagnostics (2nd 0 x-1)
2. Enter your data in L1 and L2
3. Look at the data you have entered. What is the
temperature doing? Now let’s actually look at the STAT
PLOT (Zoom 9).
4. Which function that we’ve studied would best model
the data?
STAT CALC 5
What is the r2 value?
r2 = .927
This tells us that 92.7%
of the time, the model is
a good predictor, and the
closer this value is to 1,
the closer the data is to
the model.
Analysis
to the model, what month does
 According
the maximum temperature occur?

June!
to the model, during what
 According
months would the temperature be 50°?

March and October
Donald is standing on top of the bleachers and
throws a football across the field. The data that
follows gives the height of the ball in feet versus the
seconds since the ball was thrown.
Time
0.2 0.6 1 1.2 1.5 2 2.5 2.8 3.4 3.8 4.5
Ht.       92 110 130 134 142 144 140 132 112 90                                   44
a. Show a scatter plot of the data. What is the independent variable, and
what is the dependent variable?
b. What prediction equation (mathematical model) describes this data?
c. When will the ball be at a height of 150 feet?
d. When will the ball be at a height of 100 feet?
e. At what times will the ball be at a height greater than 100 feet?
f. When will the ball be at a height of 40 feet?
g. When will the ball hit the ground?
a. Show a scatter plot of the data. What is
the independent variable, and what is the
dependent variable?

Independent variable (x): Time! (always!)
Dependent variable (y):    Height
b. What prediction equation
(mathematical model) describes
this data?

c. When will the ball be at a height
of 150 feet?
 Height (y)
 Put 150 in y2.

What happened?!? Explain.
d. When will the ball be at a height
of 100 feet?

   Put 100 in y2 and find the intersection!

.34 seconds
and
3.65 seconds
e. At what times will the ball be at
a height greater than 100 feet?

.34  x  3.65
f. When will the ball be at a height
of 40 feet?

4.53 seconds
g. When will the ball hit the
ground?

Put 0 in y2 and find the intersection!

4.98 seconds
Now try it on
Miranda throws a set of keys       1. Answer parts a),
up to her brother, who is          b), and c).
standing on a third-story
balcony with his hands 38        2. Then write a
feet about the ground. If          paragraph (with
Miranda throws the key with          complete
an initial velocity of 40 feet
per second, the following          sentences!) that
equation gives the height h         tells me exactly
of the keys after t seconds:        what you did.
h( x)  0.1x  1.18 x  2
should give the
a)  How long does it take the         exact directions
keys to reach their highest        so that someone
point?