7 6 Practice Continued for Use With Pages 512 522 Slader
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Lesson 7.6 , For use with pages 515-522 PowerPoint Presentation
Lesson 7.6 , For use with pages 515-522
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Lesson 7.6 , For use with pages 515-522
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WARMUP –5, 12 ANSWER ANSWER ANSWER 34 = 2x – 7 3 2 1 log8 30 = x ANSWER ANSWER 125 Lesson 7.6, For use with pages 515-522 1.Write log3(2x – 7) = 4 in exponential form. • Write 8x= 30 in logarithmic form. • Hint: reverse loop swoop doop Solve for x. 3. 100x= 1000 4.log5x = –3 • x2 – 7x – 60 = 0 • Hint: Use the quadratic formula.
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7.6 Notes - Solve Exponential and Log Equations https://www.youtube.com/watch?v=XjzBpJ1XYwc
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Rewrite each base as a power of 2. Distribute. Powers equal to each other. Objective - To solve exponential and logarithmic equations.
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Take the log3 of each side.
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Take the log5 of each side.
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If logb x = logb y if and only if x = y.
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Loop Swoop Doop
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You do this one If x = y, then bx = by. You probably did loop-swoop-doop, but here is another approach.
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10 Check! Remember, you can't take the log of a negative!
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1 x –3 x 2 Solve 4= x –3 2 x – x +3 x 2 = 2 1 1 4= Rewrite 4 and as powers with base 2. 2 2 x x –3 2 –1 (2 ) = (2 ) ANSWER The solution is 1. EXAMPLE 1 Solve by equating exponents SOLUTION Write original equation. Power of a power property Property of equality for exponential equations 2x = –x + 3 x = 1 Solve for x.
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–2 ? 4 = 1 1 2 2 1–3 ? 1 4 = EXAMPLE 1 Solve by equating exponents Check: Check the solution by substituting it into the original equation. Substitute 1 for x. Simplify. Solution checks. 4 = 4
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1 – 8 3 5 5x –6 3 – x 3. 81 = x –1 2x 1. 9 = 27 7x +1 3x –2 2. 100 = 1000 for Example 1 GUIDED PRACTICE Solve the equation. SOLUTION –3 SOLUTION –6 SOLUTION
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x log 4 = log 11 4 4 Takelogof each side. 4 x = log 11 x = 11 log 4 x 4 = 11 log 4 x x Solve 4 = 11. log b = x b The solution is about 1.73. Check this in the original equation. ANSWER x 1.73 EXAMPLE 2 Take a logarithm of each side SOLUTION Write original equation. Change-of-base formula Use a calculator.
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EXAMPLE 3 Use an exponential model Cars You are driving on a hot day when your car overheats and stops running. It overheats at 280°F and can be driven again at 230°F. If r = 0.0048 and it is 80°F outside,how long (in minutes) do you have to wait until you can continue driving?
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Substitute for T, T , T, and r. R ° x x 230 = (280 – 80)e + 80 Ine = log e = x –0.0048t –0.2877 –0.0048t e –0.0048t 0.75 =e –0.0048t 150 = 200e –0.0048t ln 0.75 = ln e 60 t –rt T = ( T – T )e + T R ° R EXAMPLE 3 Use an exponential model SOLUTION Newton's law of cooling Subtract 80 from each side. Divide each side by 200. Take natural log of each side. Divide each side by –0.0048.
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ANSWER You have to wait about 60 minutes until you can continue driving. EXAMPLE 3 Use an exponential model
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9x 5. 7 = 15 x 4. 2 = 5 –0.3x 6. 4e –7 = 13 for Examples 2 and 3 GUIDED PRACTICE Solve the equation. SOLUTION about 2.32 about 0.155 SOLUTION SOLUTION about–5.365
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log (4x – 7) = log (x + 5). 5 5 Solve log (4x – 7) = log (x + 5). 5 5 ANSWER The solution is 4. EXAMPLE 4 Solve a logarithmic equation SOLUTION Write original equation. 4x – 7 = x + 5 Property of equality for logarithmic equations 3x – 7 = 5 Subtract xfrom each side. 3x = 12 Add 7 to each side. x = 4 Divide each side by 3.
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(4x – 7) = (x – 5) ? (4 4 – 7) = (4 + 5) 9 = 9 log log log log log log 5 5 5 5 5 5 EXAMPLE 4 Solve a logarithmic equation Check: Check the solution by substituting it into the original equation. Write original equation. Substitute 4 for x. Solution checks.
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Solve (5x – 1)= 3 (5x – 1)= 3 (5x – 1)= 3 4log4(5x – 1) = 4 log log log 4 4 b ANSWER x The solution is 13. b = x EXAMPLE 5 Exponentiate each side of an equation SOLUTION Write original equation. Exponentiate each side using base 4. 5x – 1 = 64 5x = 65 Add 1 to each side. x = 13 Divide each side by 5.
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Check: (5x – 1) = (5 13 – 1) = 64 log log log log 4 4 4 4 3 Because 4 = 64, 64= 3. EXAMPLE 5 Exponentiate each side of an equation
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log [2x(x – 5)] 2 10 = 10 EXAMPLE 6 Standardized Test Practice SOLUTION log 2x +log(x – 5) = 2 Write original equation. log [2x(x – 5)] = 2 Product property of logarithms Exponentiate each side using base 10. 2x(x – 5) = 100 Distributive property
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2 x – 5x – 50 = 0 log b 2 2x – 10x – 100 = 0 2 2x – 10x = 100 x b = x EXAMPLE 6 Standardized Test Practice Write in standard form. Divide each side by 2. (x – 10)(x + 5) = 0 Factor. x = 10 orx = – 5 Zero product property Check: Check the apparent solutions 10 and –5 using algebra or a graph. Algebra: Substitute 10 and –5 for xin the original equation.
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log (2 10) + log (10 – 5) = 2 2 = 2 EXAMPLE 6 Standardized Test Practice log 2x + log (x – 5) = 2 log 2x+ log (x– 5) = 2 log [2(–5)] + log (–5– 5) = 2 log (–10) + log (–10) = 2 log 20 + log 5 = 2 Because log (–10) is not defined, –5 is not a solution. log 100 = 2 So, 10 is a solution.
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ANSWER The correct answer is C. EXAMPLE 6 Standardized Test Practice Graph: Graph y = log 2x + log (x – 5) andy = 2 in the same coordinate plane. The graphs intersect only once, when x = 10. So, 10 is the only solution.
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10.log (x + 12) + log x =3 4 4 8.log(x – 6) = 5 2 for Examples 4, 5 and 6 GUIDED PRACTICE Solve the equation. Check for extraneous solutions. 7. ln (7x – 4) = ln (2x + 11) 9. log 5x + log (x – 1) = 2 SOLUTION 5 SOLUTION 3 4 SOLUTION SOLUTION 38
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The apparent magnitude of a star is a measure of the brightness of the star as it appears to observers on Earth. The apparent magnitude Mof the dimmest star that can be seen with a telescope is given by the function Astronomy EXAMPLE 7 Use a logarithmic model M = 5 logD + 2 where Dis the diameter (in millimeters) of the telescope's objective lens. If a telescope can reveal stars with a magnitude of 12, what is the diameter of its objective lens?
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2 Log D 10 = 10 ANSWER The diameter is 100 millimeters. EXAMPLE 7 Use a logarithmic model SOLUTION M = 5 log D + 2 Write original equation. 12 = 5 log D + 2 Substitute 12 for M. 10 = 5 log D Subtract 2 from each side. 2 = log D Divide each side by 5. Exponentiate each side using base 10. 100 = D Simplify.
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for Example 7 GUIDED PRACTICE 11.WHAT IF?Use the information from Example 7 to find the diameter of the objective lens of a telescope that can reveal stars with a magnitude of 7. SOLUTION The diameter is 10 millimeters.
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7.6 Assignment Hint #3: Quadratic Formula
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6 16 ANSWER ANSWER 5 5 about 0.77 ANSWER ANSWER about 13min ANSWER ANSWER 9 WARMUP Daily Homework Quiz For use after Lesson 7.6 Solve. 1.25x= 125–x + 2 2.8x = 5 3.log7(5x– 8) =log7 (2x + 19) 4.log3 (5x+ 1) = 4 5.log5 5x + log5 (x– 4) = 2 Bonus.Boiling water has a temperature of 212° F. Water has a cooling rate of r = 0.042. Use the formula T = (T0 –TR)e –rt + TRto find the number of minutes tit will take for the water to cool to a temperature of 80°F if the room temperature is 72°F.
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Chapter 7 Test Review Assignment p.541: 17-20 all, 24-34 all (16 Q's) Chapter Test p.543: 10-12 all, 16-24 all, 28 (A = Pert) (13 Q's) Do as much as you can without a calculator. Use your calculator to check (if not in the back)
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Answers to the Review (p.541) 16 Q's 28. ln 3 + ln y – 5 ln x 29. log7 384 30. ln(12/x2) 31. ln36 32. 2.153 33.7 34. 3.592 • 5 • 0 • -3 • -1/3 • 6.86mm, 5.39mm • log83 + log8 x + log8 y • ln10 + 3ln x + ln y • log8 – 4 log y • ln 3 + ln y – 5 ln x
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Answers to the Test (p.543) 13 Q's • 1.732 • 0.874 • 104 • 2 28. $3307.82 • 2 • -5 • 0 16. ln(49/64) 17. log496 • log(5x/9) • 2.431 • 1.750
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