# Exponential & Logarithmic Functions - PowerPoint PPT Presentation

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Exponential & Logarithmic Functions. Table of Contents. Exponential Functions Logarithmic Functions Converting between Exponents and Logarithms Properties of Logarithms Exponential and Logarithmic Equations. General Form of Exponential Function y = b x where b > 1.

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Exponential & Logarithmic Functions

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## Exponential & Logarithmic Functions

• Exponential Functions

• Logarithmic Functions

• Converting between Exponents and Logarithms

• Properties of Logarithms

• Exponential and Logarithmic Equations

### General Form of Exponential Function y = b x where b > 1

• Domain: All reals

• Range:

y > 0

• x-intercept: None

• y-intercept: (0, 1)

### General Form of Exponential Functiony = b (x + c) + dwhere b > 1

• c moves graph left or right (opposite way)

• d move graph up or down (expected way)

• So y=3(x+2) + 3 moves the graph 2 units to the left and 3 units up

• (0, 1) to (– 2, 4)

### Relationships of Exponential (y = bx) & Logarithmic (y = logbx) Functions

• y = logbx is the inverse of y = bx

• Domain: x > 0

• Range: All Reals

• x-intercept: (1, 0)

• y-intercept: None

• y = bx

• Domain: All Reals

• Range: y > 0

• x-intercept: None

• y-intercept: (0, 1)

### Relationships of Exponential (y = bx) & Logarithmic (y = logbx) Functions

BASEEXPONENT = POWER

42 = 16

4 is the base. 2 is the exponent. 16 is the power.

As a logarithm, logBASEPOWER=EXPONENT

log 4 16 = 2

### Logarithmic Abbreviations

• log10 x = log x (Common log)

• loge x = ln x (Natural log)

• e = 2.71828...

logb(MN)= logbM + logbN

Ex: log4(15)= log45 + log43

logb(M/N)= logbM – logbN

Ex: log3(50/2)= log350 – log32

logbMr = r logbM

Ex: log7 103 = 3 log7 10

logb(1/M) = logbM-1= –1 logbM = – logbM

log11 (1/8) = log11 8-1 = – 1 log11 8 = – log11 8

### Properties of Logarithms (Shortcuts)

• logb1 = 0 (because b0 = 1)

• logbb = 1 (because b1 = b)

• logbbr = r (because br = br)

• blog b M = M (because logbM= logbM)

### Examples of Logarithms

• Simplify log 7 + log 4 – log 2 =

log 7*4 = log 14 2

• Simplify ln e2=

2 ln e = 2 logee = 2 * 1 = 2

• Simplify e 4 ln 3 - 3 ln 4=

e ln 34 - ln 43 = e ln 81/64 = e loge81/64 = 81/64

logam

logbm = --------

logab

log712 = log 12

log 7

OR

### Change-of-Base Formula

• log712= ln 12

• ln 7

### Exponential & Logarithmic Equations

• If logb m = logb n, then m = n.

If log6 2x = log6(x + 3), then 2x = x + 3 and x = 3.

• If bm = bn, then m = n.

If 51-x = 5-2x, then 1 – x = – 2x and

x = – 1.

### If your variable is in the exponent…..

• Isolate the base-exponent term.

• Write as a log. Solve for the variable.

• Example: 4x+3 = 7

• log4 7 = x + 3 and – 3 + log4 7 = x

OR with change of bases:

x = – 3 + log 7 log 4

• Another method is to take the LOG of both sides.

### Logarithmic Equations

• Isolate to a single log term.

• Convert to an exponent.

• Solve equation.

• Example: log x + log (x – 15) = 2

• log x(x – 15) = 2 so 102 = x (x – 15) and

100 = x2 – 15x and 0 = x2 – 15x – 100

So 0 = (x – 20) (x + 5) so x = 20 or – 5