Logarithmic function Done By: Al-Hanoof Amna Dana Ghada

Logarithmic Function Changing from Exponential to Logarithmic form. ( Ghada ) Graphing of Logarithmic Function.( Amna ) Common Logarithm.( Ghada ) Natural Logarithm.( Ghada ) Laws of Logarithmic Function. ( Dana ) Change of the base.( Ghada ) Solving of Logarithmic Function.( Al-Hanoof ) Application of Logarithmic Function.(Al-Hanoof)

Logarithmic Function Every exponential function f(x) = a x, with a > 0 and a ≠ 1. is a one- to-one function, therefore has an inverse function(f-1). The inverse function is called the Logarithmic function with base a and is denoted by Log a Let a be a positive number with a ≠ 1. The logarithmic function with base a, denoted by loga is defined by: Log a x = y a y = Х Clearly, Loga Х is the exponent to which the base a must be raised to give Х

Logarithmic Function Logarithmic form Exponential form Exponent Exponent Log a x = y a^ y = Х Base Base

Logarithmic Function Example: Logarithmic form Log 2 8= 3 Exponential form 2^3=8

Logarithmic Function  Graphs of Logarithmic Functions: The exponential function f(x) =a^x has Domain: IR Range: (0.∞), Since the logarithmic function is the inverse function for the exponential function, it has Domain : (0, ∞) Range: IR.

Logarithmic Function The graph of f(x) = Log a x is obtained by reflecting the graph of f(x) = a^ x the line y = x x-intercept of the function y = Log a x is 1 f(x) = a^ x y = x

Logarithmic Function This is the basic function y= Loga x y = log a x

Logarithmic Function y =- log a x The function is reflected in the x-axis.

Logarithmic Function y = log2 (-x) The function is reflected in the y-axis.

Logarithmic Function The function is shifted to the left by two unites. Y=log a (x+2)

Logarithmic Function The function is shifted to the right by two unites. y = log a (x-2)

Logarithmic Function The function is shifted to the upward by two unites. y = log a x +2

Logarithmic Function y = log a x -2 The function is shifted to the downward by two unites.

Logarithmic Function Example: Finding the domain of a logarithmic function: F(x)=log(x-2) Solution: As any logarithmic function lnx is defined when x>0, thus,the domain of f(x) is x-2 >0 X>2 So the domain =(2,∞)

Logarithmic Function  Common Logarithmic; The logarithm with base 10 is called the common logarithm and is denoted by omitting the base: log x = log 10 x  Natural Logarithms: The logarithm with base e is called the natural logarithm and is denoted by In: ln x =log e x

Logarithmic Function The natural logarithmic function y = In x is the inverse function of the exponential function y = e^X.By the definition of inverse functions we have: ln x =y e^y=x Y=e^x Y=ln x

Laws of logarithms: Let a be a positive number, with a≠1. let A>0, B>0, and C be any real numbers. 1.log a (AB) = log a A + log a B log 2 (6x) = log log 2 x 2.log a (A/B) = log a A - log a B log 2 (10/3) = log 2 10 – log log a A^c = C log a A log 3 √5 = log 3 51/2 = 1/2 log3 5 Logarithmic Function

Rewrite each expression using logarithm laws log 5 (x^3 y^6) = log 5 x^3 + log 5 y^6 law1 = 3 log 5 x + 6 log 5 y law3 ln (ab/3√c) = ln (ab) – ln 3√c law2 = ln a + ln b – ln c1/3 law1 = ln a + ln b – 1/3 ln c law3 Logarithmic Function

Express as a single logarithm 3 log x + ½ log (x+1) = log x^3 + log (x+1)^1/2 law3 =log x^3(x+1)^1/2 law1 3 ln s + ½ ln t – 4 ln (t2+1) = ln s^3 + ln t^1/2 – ln (t^2+1)^4 law3 = ln ( s^3 t^1/2) – ln (t^2 + 1)^4 law1 = ln s^3 √t /(t2+1)^4 law2 Logarithmic Function

*WARNING: log a (x+y) ≠ log a x +log a y Log 6/log2 ≠ log(6/2) (log2x)3 ≠ 3log2x

Logarithmic Function  Change of Base: Sometimes we need to change from logarithms in one base to logarithms in another base. b^y = x (exponential form) log a b^y = log a x (take loga for both sides) y log a b =log a x (law3) y=(log a x)/(log a b) (divide by logab)

Logarithmic Function Example: Since all calculators are operational for log10 we will change the base to 10 Log 8 5 = log 10 5/ log 10 8≈ (approximating the answer by using the calculator)

Logarithmic Function Solving the logarithmic Equations: Example: Find the solution of the equation log 3^(x+2) = log7. SOLUTION: (x + 2) log 3=log7 (bring down the exponent) X+2= log7 (divide by log 3 ) log 3 x = log7 -2 (subtract by 2) log3

Logarithmic Function  Application of e and Exponential Functions: In the calculation of interest exponential function is used. In order to make the solution easier we use the logarithmic function. A= P (1+ r/n)^nt A is the money accumulated. P is the principal (beginning) amount r is the annual interest rate n is the number of compounding periods per year t is the number of years There are three formulas: A = p(1+r) Simple interest (for one year) A(t) = p(1+r/n)nt Interest compounded n times per year A(t) = pert Interest compounded continuously

Logarithmic Function Example: A sum of $500 is invested at an interest rate 9%per year. Find the time required for the money to double if the interest is compounded according to the following method. a) Semiannual b) continuous Solution: (a) We use the formula for compound interest with P = $5000, A (t) = $10,000 r = 0.09, n = 2, and solve the resulting exponential equation for t. (1.045)^2t = 2 (Divide by 5000) log ( )^2t = log 2 (Take log of each side) 2t log = log 2 Law 3 (bring down the exponent) t= (log 2)/ (2 log 1.045) (Divide by 2 log 1.045) t ≈ 7.9 The money will double in 7.9 years. (using a calculator)

Logarithmic Function (b) We use the formula for continuously compounded interest with P = $5000, A(t) = $10,000, r = 0.09, and solve the resulting exponential equation for t. 5000e^0.09t = 10,000 e^0.091 = 2 (Divide by 5000) In e0.091 = In 2 (Take 10 of each side) 0.09t = In 2 (Property of In) t=(In 2)/(0.09) (Divide by 0.09) t ≈7.702 (Use a calculator) The money will double in 7.7 years.