VIEWS: 5 PAGES: 27 POSTED ON: 10/8/2011
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 the basket? (10 feet) c) When will the ball hit the floor, if it missed the basket entirely? 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! Answer: 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! Answer: 2.4 seconds! c) When will the ball hit the floor, if it missed the basket entirely? 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? Do a quadratic regression! 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? QUADRATIC!! 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 your own! 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 2 Your paragraph should give the a) How long does it take the exact directions keys to reach their highest so that someone point? could read what b) How high do the keys reach? you wrote and c) Will her brother be able to get the right catch the keys, why or why answers to all not? three parts.