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Higher Outcome 3 Higher Unit 3 Exponential & Log Graphs Special “e” and Links between Log and Exp Rules for Logs Exam Type Questions Solving Exponential Equations Experimental & Theory Harder Exponential & Log Graphs

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Higher Outcome 3 The Exponential & Logarithmic Functions Exponential Graph Logarithmic Graph y x y x (0,1) (1,0)

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Higher Outcome 3 The letter e represents the value 2.718….. (a never ending decimal). This number occurs often in nature f(x) = x = e x is called the exponential function to the base e. A Special Exponential Function – the “Number” e

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Higher Outcome 3 In Unit 1 we found that the exponential function has an inverse function, called the logarithmic function. The log function is the inverse of the exponential function, so it ‘undoes’ the exponential function: Linking the Exponential and the Logarithmic Function

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Higher Outcome Linking the Exponential and the Logarithmic Function

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Higher Outcome Examples (a)log 3 81 = “ to what power gives ?” (b)log 4 2 = “ to what power gives ?” (c)log 3 =“ to what power gives ?” Linking the Exponential and the Logarithmic Function

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Higher Outcome 3 Rules of Logarithms Three rules to learn in this section

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Higher Outcome 3 Examples Simplify: a)log log b)log 3 63 – log 3 7 Rules of Logarithms Since

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Higher Outcome 3 Example Since Rules of Logarithms Since

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Higher Outcome 3 You have 2 logarithm buttons on your calculator: which stands for log 10 which stands for log e log ln Try finding log on your calculator 2 Using your Calculator and its inverse and its inverse

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Higher Outcome 1 Logarithms & Exponentials We have now reached a stage where trial and error is no longer required! Solvee x = 14 (to 2 dp) ln(e x ) = ln(14) x = ln(14) x = 2.64 Check e 2.64 = Solveln(x) = 3.5 (to 3 dp) e lnx = e 3.5 x = e 3.5 x = Check ln = April April April 2015www.mathsrevision.com

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Higher Outcome 1 Solve 3 x = 52 ( to 5 dp ) ln3 x = ln(52) xln3 = ln(52)(Rule 3) x = ln(52) ln(3) x = Check: = …. 17 April April April 2015www.mathsrevision.com Logarithms & Exponentials

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Higher Outcome 3 Solve 5 1 = 5 and 5 2 = 25 so we can see that x liesbetween 1 and 2 Taking logs of both sides and applying the rules Solving Exponential Equations Since Example

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Higher Outcome 3 For the formula P(t) = 50e -2t : a)Evaluate P(0) b)For what value of t is P(t) = ½P(0)? Solving Exponential Equations (a) Remember a 0 always equals 1 Example

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Higher Outcome 3 For the formula P(t) = 50e -2t : b)For what value of t is P(t) = ½P(0)? Solving Exponential Equations ln = log e e log e e = 1 Example

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Higher Outcome 3 The formula A = A 0 e -kt gives the amount of a radioactive substance after time t minutes. After 4 minutes 50g is reduced to 45g. (a) Find the value of k to two significant figures. (b) How long does it take for the substance to reduce to half it original weight? Example (a) Solving Exponential Equations

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Higher Outcome 3 (a) Solving Exponential Equations Example

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Higher Outcome 3 Solving Exponential Equations ln = log e e log e e = 1 Example

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Higher Outcome 3 (b) How long does it take for the substance to reduce to half it original weight? Solving Exponential Equations ln = log e e log e e = 1 Example

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Higher Outcome 3 When conducting an experiment scientists may analyse the data to find if a formula connecting the variables exists. Data from an experiment may result in a graph of the form shown in the diagram, indicating exponential growth. A graph such as this implies a formula of the type y = kx n Experiment and Theory y x

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Higher Outcome 3 We can find this formula by using logarithms: If Then So Compare this to So Is the equation of a straight line Experiment and Theory log y log x (0,log k)

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Higher Outcome 3 Experiment and Theory From We see by taking logs that we can reduce this problem to a straight line problem where: And log y log x (0,log k) YmXc=+ Y Xcm

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Higher Outcome 3 ln(y) ln(x) m = Express y in terms of x. NB: straight line with gradient 5 and intercept 0.69 UsingY = mX + c ln(y) = 5ln(x) ln(y) = 5ln(x) + ln(e 0.69 ) ln(y) = 5ln(x) + ln(2) ln(y) = ln(x 5 ) + ln(2) ln(y) = ln(2x 5 ) y = 2x 5 Experiment and Theory

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Higher Outcome 1 log 10 y log 10 x Find the formula connecting x and y. straight line with intercept 0.3 Using Y = mX + c Taking logs log 10 y = -0.3log 10 x log 10 y = -0.3log 10 x + log log 10 y = -0.3log 10 x + log 10 2 log 10 y = log 10 x log 10 2 log 10 y = log 10 2x -0.3 y = 2x -0.3 m = -0.3 / 1 = -0.3 Experiment and Theory

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Higher Outcome 1 Experimental Data When scientists & engineers try to find relationships between variables in experimental data the figures are often very large or very small and drawing meaningful graphs can be difficult. The graphs often take exponential form so this adds to the difficulty. By plotting log values instead we often convert from

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Higher Outcome 3 The variables Q and T are known to be related by a formula in the form The following data is obtained from experimenting Q T Plotting a meaningful graph is too difficult so taking log values instead we get …. log 10 Q log 10 T T = kQ n

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log 10 Q log 10 T m = = 4 Point on line (a,b) = (1,3.7)

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Higher Outcome 3 Since the graph does not cut the y-axis use Y – b = m(X – a) where X = log 10 Q and Y = log 10 T, log 10 T – 3.7 = 4(log 10 Q – 1) log 10 T – 3.7 = 4log 10 Q – 4 log 10 T = 4log 10 Q – 0.3 log 10 T = log 10 Q 4 – log log 10 T = log 10 Q 4 – log 10 2 log 10 T = log 10 ( Q 4 / 2 ) T = 1 / 2 Q 4 Experiment and Theory

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Higher Outcome 3 Example The following data was collected during an experiment: a) Show that y and x are related by the formula y = kx n. b) Find the values of k and n and state the formula that connects x and y. X y Experiment and Theory

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Higher Outcome 3 a)Taking logs of x and y and plotting points we get: Since we get a straight line the formula connecting X and Y is of the form X y

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Higher Outcome 3 b) Since the points lie on a straight line, formula is of the form: Graph has equation Compare this to Experiment and Theory Selecting 2 points on the graph and substituting them into the straight line equation we get:

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Higher Outcome 3 Sub in B to find value of c Experiment and Theory Sim. Equations Solving we get The two points picked are and ( any will do ! )

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Higher Outcome 3 So we have Compare this to andso Experiment and Theory

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Higher Outcome 3 solving so You can always check this on your graphics calculator Experiment and Theory

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Higher Outcome 3 Transformations of Log & Exp Graphs In this section we use the rules from Unit 1 Outcome 2 Here is the graph of y = log 10 x. Make sketches of y = log x andy = log 10 ( 1 / x ).

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Higher Outcome 3 log x = log log 10 x= log log 10 x = 3 + log 10 x If f(x) = log 10 x then this is f(x) + 3 y = log x Graph Sketching (10,1) (1,0) (1,3) (10,4) y = log 10 x

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Higher Outcome 3 Graph Sketching log 10 ( 1 / x ) = log 10 x -1 = -log 10 x If f(x) = log 10 x-f(x) ( reflect in x - axis ) (1,0) (10,1) (10,-1) y = log 10 x y = -log 10 x

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Higher Outcome 3 Here is the graph of y = e x y = e x Sketch the graph of y = -e (x+1) Graph Sketching (0,1) (1,e)

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Higher Outcome 3 If f(x) = e x reflect in x-axismove 1 left y = -e (x+1) Graph Sketching (-1,1) (0,-e) -e (x+1) = -f(x+1)

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Revision Logarithms & Exponentials Higher Mathematics Next

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Logarithms Revision Back Next Quit Reminder All the questions on this topic will depend upon you knowing and being able to use, some very basic rules and facts. Click to show When you see this button click for more information

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Logarithms Revision Back Next Quit Three Rules of logs

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Logarithms Revision Back Next Quit Two special logarithms

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Logarithms Revision Back Next Quit Relationship between log and exponential

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Logarithms Revision Back Next Quit Graph of the exponential function

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Logarithms Revision Back Next Quit Graph of the logarithmic function

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Logarithms Revision Back Next Quit Related functions of Move graph left a units Move graph right a units Reflect in x axis Reflect in y axis Move graph up a units Move graph down a units Click to show

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Logarithms Revision Back Next Quit Calculator keys lnln = l og =

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Logarithms Revision Back Next Quit Calculator keys lnln = 2.5= = 0.916… l og = 7.6= = … Click to show

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Logarithms Revision Back Next Quit Solving exponential equations Show Take log e both sides Use log ab = log a + log b Use log a x = x log a Use log a a = 1

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Logarithms Revision Back Next Quit Solving exponential equations Take log e both sides Use log ab = log a + log b Use log a x = x log a Use log a a = 1 Show

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Logarithms Revision Back Next Quit Solving logarithmic equations Change to exponential form Show

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Logarithms Revision Back Next Quit Simplify expressing your answer in the form where A, B and C are whole numbers. Show

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Logarithms Revision Back Next Quit Simplify Show

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Logarithms Revision Back Next Quit Find x if Show

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Logarithms Revision Back Next Quit Givenfind algebraically the value of x. Show

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Logarithms Revision Back Next Quit Find the x co-ordinate of the point where the graph of the curve with equation intersects the x -axis. When y = 0 Exponential form Re-arrange Show

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Logarithms Revision Back Next Quit The graph illustrates the law If the straight line passes through A(0.5, 0) and B(0, 1). Find the values of k and n. Gradient y-intercept Show

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is the area covered by the fire when it was first detected and A is the area covered by the fire t hours later. If it takes one and a half hours for the area of the forest fire to double, find the value of the constant k. Logarithms Revision Back Next Quit Before a forest fire was brought under control, the spread of fire was described by a law of the form where Show

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Logarithms Revision Back Next Quit The results of an experiment give rise to the graph shown. a)Write down the equation of the line in terms of P and Q. It is given that and stating the values of a and b. b) Show that p and q satisfy a relationship of the form Gradient y-intercept Show

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Logarithms Revision Back Next Quit The diagram shows part of the graph of. Determine the values of a and b. Use (7, 1) Use (3, 0) Hence, from (2) and from (1) Show

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Logarithms Revision Back Next Quit The diagram shows a sketch of part of the graph of a)State the values of a and b. b)Sketch the graph of Graph moves 1 unit to the left and 3 units down Show

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Logarithms Revision Back Next Quit a) i) Sketch the graph of ii) On the same diagram, sketch the graph of b)Prove that the graphs intersect at a point where the x-coordinate is Show

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Logarithms Revision Back Next Quit Part of the graph of is shown in the diagram. This graph crosses the x-axis at the point A and the straight line at the point B. Find algebraically the x co-ordinates of A and B. Show

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Logarithms Revision Back Next Quit The diagram is a sketch of part of the graph of a)If (1, t ) and ( u, 1) lie on this curve, write down the values of t and u. b)Make a copy of this diagram and on it sketch the graph of c)Find the co-ordinates of the point of intersection of with the line a) b) c) Show

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Logarithms Revision Back Next Quit The diagram shows part of the graph with equation and the straight line with equation These graphs intersect at P. Solve algebraically the equation and hence write down, correct to 3 decimal places, the co-ordinates of P. Show

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Higher Outcome 3 Are you on Target ! Update you log book Make sure you complete and correct ALL of the Logs and Exponentials questions in the past paper booklet.Logs and Exponentials

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