Monday, December 15, 2008

Okay, so the beginning of class we talked about how the y-intercept is the point where the line crosses the y axis. Slope is rise over run, but what the slop means depends on the question. For example, the yearbook question that we did, the slope equaled 12, which meant that a yearbook costs 12 dollars. Or the taxi question we did, where the slope equaled 1, that meant that the taxi costs $1 per km. Then we went on and talked about the question we started on friday about the antibacterial spray. The first thing we had to do with that question was set it up. First you plot all the points on your calculator by pressing STAT then press ENTER. Then you just add all of the number of hours (x) in the first list, and the number of bacteria (y) in the second list. The first two questions ask you to find the slope, the y-intercept and what they mean/represent. To answer this, you have to use a linear regression equation. To do this you press STAT and then the right arrow key to slide over to CALC, then you press 4 to get LinReg(ax+b) on the home screen. Once you have that you press 2nd and 1 (it's for the first list you entered number of hours in) then press the comma key, which is just above the number 7, then press 2nd and 2 (for the second list). Then you will put another comma and press VARS arrow key right to get to Y-VARS then press ENTER, and press ENTER again. For the first question, you need to find the slope, if your on the home screen with your linear regression equation showing press ENTER and you will see your slope and your y-intercept. Your slope is a and your y-intercept is b. The slope that you should see is -4.9. It means that the bacteria decreases more and more and time goes on. The next question askes what the y-intercept is and what it represents. If you look it should be 99.14, and that is how many bacteria is there before they sprayed there antibacterial spray. The next question you have to write out the equation, which will be Y=-4.93+99.14, but you want it more realistic, so you would write it as N(h)= -4.93+99.14. (N meaning number of bacteria, and h meaning hours.) The next question asks after how many hours would 25 bacteria be present? To answer this question, press GRAPH. If you need to adjust your window, then press WINDOW.

<-- Enter these values, and your window should fit just right. Press Y= and go down to Y2= and enter 25. This will make it so that on the Y axis ther will always be a line at 25.
Press GRAPH again, then press 2nd and CALC (above TRACE). Then press 5 which is intersect. Move your right arrow down to where the lines intersect, (your X should be around 14.9 and your Y 25.7) and at the bottom of the screen it should say First Curve? Now you press ENTER and it should now say Second Curve? Press ENTER once again and it should say Guess? Press ENTER for the last time, and it should say Intersection, and now your done. Notice how your Y=25 and your X=15.04. That means that the bacteria that is present is 25, and the hours it took to get there is 15. The next question is asking to state the largest value and the smallest value of the domain. (Domain is the X axis). To do this you have to 2nd CALC and then press 2 because you are looking for zero. Then you press the right arrow to scroll down on your line until you get to the X axis. When you are there, the coordinates should be around 19.9 for X and .834
for Y. To make sure that you have the point in the right place, your Y should be just under zero. Your screen should be saying Left Bound? at the bottom, so press ENTER (when your over the right place) and it should now say Right Bound? Then your going to move your right arrow over just once so that your Y is now a negative number. Press ENTER again so that it will say Guess? then press ENTER one more time. Your screen should now say Zero and your X axis should be at 20.12. For this question your smallest value is 0, and your largest value is 20.12. For the next question is asks for the largest value and the smallest value of the range. (Range is the Y axis). For this question you just need to look at the graph and see that your smallest value is 0 and your largest value is 99.14. You know this because the number of bacteria has to be 0, you can't go any less than that, and the largest number is 99.14 because that is the y-intercept. That is all of the questions that was on that paper. Thanks for reading this all! (:


Anonymous said...

Wow this is pretty helpful Paige
it looks like you've worked pretty hard on it :)