Math Check courseware for due dates for Homework, Quizzes, Poppers, Practice test and Tests. Previous lecture

Transcription

1 Math 1311 Check courseware for due dates for Homework, Quizzes, Poppers, Practice test and Tests Previous lecture Section 2.4: Solving Nonlinear Equations Equations that involve powers (other than one), radicals (such as square roots), exponential terms, etc. are called nonlinear equations. Some such equations have algebraic ways in which they can be solved. For most nonlinear equations, we will focus on graphical techniques (using the TI calculator). Crossing Graphs Method 1. Press, enter the one side of the equation in YY 1 and the other side in YY 2 2. Use the table to get a get an approximation of where the solution(s) is/are 3. Press, set Xmin and Xmax so that the solution(s) are between them 4. Press to see the graph 5. Press and choose 5: intersect and follow the on screen directions Example : Solve the equation xx = 85

2 Solve each of the following using the crossing graphs. xx 2 xx = xx5 20 xx = Xmin = Xmax = xx + 3 xx = 2 xx + 1 xx = Xmin = Xmax = 5 xx 2 +xx+1 = 1 there are two solution. Find both xx = Xmin = Xmax =

3 Solve using the crossing-graphs method: 12 x + 3x = 9 x + 3. Round your answer to two decimal places. Solve 6 7x = x for x. Page 3 of 9

4 Section 2.6: Optimization Optimization refers to finding the best value for a particular quantity, usually finding the largest or smallest function value for a particular situation. A function ff(xx) has a maximum (local maximum) at xx = cc if ff(cc) is bigger than ff(xx) for any xx in an interval around cc. A function ff(xx) has a minimum (local minimum) at xx = bb if ff(bb) is smaller than ff(xx) for any xx in an interval around bb. The easiest way to find a local maximum (high point) or local minimum (low point) is to look at a graph of the function in the interval of interest. Finding the maximum and/or minimum value of a function is called optimization. When we graph a function on our graphing calculator, the calculator can do the math necessary to find the maximum and minimum in the interval of interest. Skill #1 Finding a Max or Min in the graphing window 1. Put the function s formula in YY Use a table (we learned how to make these in the calculator earlier) to find an xx range. 3. We are looking for where the yy values change from increasing to decreasing or from decreasing to increasing. 4. Press and set Xmin and Xmax based on step 2, then press 5. Press and choose 3: minimum or 4: maximum Then follow the on screen directions. Page 4 of 9

5 Example 1: Below we find the maximum of ff(xx) = 32 xx xx2 ee So the maximum point is about (16, ). Example 2: A cannonball is fired into the air. The height of the cannonball (in feet) when the cannonball has traveled x feet horizontally is (xx) = xx 32 xx Find the maximum height of the cannonball. How far does the cannonball travel horizontally before achieving this height? Page 5 of 9

6 Skill #2 When a max or min occurs at and endpoint. Some functions (for our purposes almost all functions) are guaranteed to have both a maximum and minimum value when looked at only on a closed, bounded interval [aa, bb]. 1. Put the function in Y1 2. Press and set Xmin and Xmax as given in the problem 3. Press 4. If the max and/or min value occur at a peak or valley, use the technique discuss above to find this optimal value. If the max and/or min occur at the beginning or end of the graph, then while tracing the graph; enter the x value of the appropriate endpoint. Example 3: Below we find the maximum and minimum of yy = xx 3 9xx on the interval [0, 10]. Page 6 of 9

7 Example 4: Radium-223 is a radioactive substance that is itself a product of the radioactive decay of thorium-227. For one experiment, the amount AA of radium present (measured in grams) after xx days is given by = 3(ee 0.038xx ee 0.059xx ). a. What was the largest amount of radium-223 present over the first 10 days of the experiment? b. What was the largest amount of radium-223 present over the first 60 days of the experiment? c. What was the smallest amount of radium-223 present over the first 60 days of the experiment? Page 7 of 9

8 Example 5: The manager of an employee health plan for a firm has studied the balance BB, in millions of dollars, in the plan account as a function of xx, the number of years since the plan was instituted. He has determined the account balance is very well modeled by the formula BB = xx 50ee 0.1xx. a. During the first 7 years of the plan, at what time was the balance greatest? What was that balance? b. During the first 7 years of the plan, at what time was the balance lowest? What was that balance? Page 8 of 9