Exam 4: Exponential and Logarithmic Functions

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Use the definition of the logarithmic function to find xx if log⁡x512=3\log _ { x } 512 = 3 .

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log⁡x512=3\log _ { x } 512 = 3 ⇔\Leftrightarrow x3=512x ^ { 3 } = 512 ⇔\Leftrightarrow x3=83x ^ { 3 } = 8 ^ { 3 } ⇔\Leftrightarrow x=8x = 8

Find the solution of the equation 2x/2=0.012 ^ { x/2 } = 0.01 correct to four decimal places.

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A

If the pH readings of an unknown substance is pH =10.4= 10.4 , find the hydrogen ion concentration. 

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pH =−log⁡[H.]=10.4= - \log \left[ \mathrm { H } ^ { .} \right] = 10.4 ⇔\Leftrightarrow [H.]=10−10.4\left[ \mathrm { H } ^ {.} \right] = 10 ^ { - 10.4 } M ≈4.0×10−11\approx 4.0 \times 10 ^ { - 11 } M

The population of a certain country was 2,345,2352,345,235 in 19851985 and 3,458,3773,458,377 in 1995.1995 . Assume that the growth is exponential. (a) Find a formula for the population tt years after 1985.1985 . (b) Find the time required for the population to double. (c) Use the data to predict the population in the year 2005.2005 .

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Find the solution of the exponential equation e[(x/4)−1=15e ^ { [ ( x / 4 ) - 1 } = 15 , correct to four decimal places.

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If f(x)=5xf ( x ) = 5 ^ { x } , show that f(x+h)−f(x)h=5x(5h−1h)\frac { f ( x + h ) - f ( x ) } { h } = 5 ^ { x } \left( \frac { 5 ^ { h } - 1 } { h } \right) .

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A radioactive substance decays in such a way that the amount of mass remaining after t days is given by the function m(t)=13e−0.015tm ( t ) = 13 e ^ { - 0.015 t } where m(t)m ( t ) is measured in kilograms. Round your answers to three decimal places. a) Find the mass at time t=0t = 0 . b) How much of the mass remains after 100 days?

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The age of an ancient artifact can be determined by the amount of radioactive carbon-14 remaining in it. If D0D _ { 0 } is the original amount of carbon-14 and D is the amount remaining, then the artifact's age A (in years) is given by A=−8267ln⁡(DD0)A = - 8267 \ln \left( \frac { D } { D _ { 0 } } \right) Find the age of an object if the amount D of carbon-14 that remains in the object is 50% of the original amount D0D _ { 0 } .

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Show that −log⁡(x+1−x)=log⁡(x+1+x)- \log ( \sqrt { x + 1 } - \sqrt { x } ) = \log ( \sqrt { x + 1 } + \sqrt { x } ) . 

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Solve the equation 2x2(3x)−5x(3x)+3x+1=02 x ^ { 2 } \left( 3 ^ { x } \right) - 5 x \left( 3 ^ { x } \right) + 3 ^ { x + 1 } = 0 .

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Use the Laws of Logarithms to rewrite the expression log⁡4(x44)\log _ { 4 } \left( \frac { x ^ { 4 } } { 4 } \right) in a form with no logarithm of a product, quotient, root, or powers.  

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If $10,000 is invested at an interest rate of 5% per year, compounded semiannually, find the value of the investment after the given number of years. (a) 5 years (b) 10 years (c) 15 years

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The age of an ancient artifact can be determined by the amount of radioactive carbon-14 remaining in it. If D0D _ { 0 } is the original amount of carbon-14 and D is the amount remaining, then the artifact's age A (in years) is given by A=−8267ln⁡(DD0)A = - 8267 \ln \left( \frac { D } { D _ { 0 } } \right) Find the age of an object if the amount D of carbon-14 that remains in the object is 85% of the original amount D0D _ { 0 } .

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A certain strain of bacteria divides every three hours. If a colony is started with 50 bacteria, then the time t (in hours) required for the colony to grow to N bacteria is given by t=3log⁡(N/50)log⁡2t = 3 \frac { \log ( N / 50 ) } { \log 2 } Find the time required for the colony to grow to five million bacteria.

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Find the exponential function whose graph is given. Find the exponential function whose graph is given.

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Rudy wants to invest $1000\$ 1000 in savings certificates that bear an interest rate of 7.5%7.5 \% compounded semiannually. How long will it take for the amount to be $1500?\$ 1500 ?

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Find the effective yield for an investment that earns 3% per year, compounded quarterly.

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Use the Laws of Logarithms to rewrite log⁡11103\log _ { 11 } \sqrt [ 3 ] { 10 } in a form with no logarithms of products, quotients, or powers.

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A kettle full of water is brought to a boil in a room with temperature 32∘32 ^ { \circ } C. After 55 minutes the temperature of the water has decreased from 100∘100 ^ { \circ } C to 80∘80 ^ { \circ } C. Find the temperature after another 55 minutes. 

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Use the change of base formula and a calculator to evaluate log⁡63.58\log _ { 6 } 3.58 correct to six decimal places.

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