Properties of Logs
Logarithm product rule
logb(x * y) = logb(x) + logb(y)

Logarithm quotient rule
logb(x / y) = logb(x) - logb(y)

Logarithm power rule
logb(xy) = y * logb(x)


The log is the inverse of the exponential function so 43 =
is the inverse of log4 64 =

Product Rule of Logs

log2 4 + log2 8 = 5

We can also solve this by multiplying the bases together and get log2 32 = 5

When we add together logs that have the same bases we can combine them by multiplying the numbers we are taking the log of.

logb (x * y) = logb x + logb y

log6 12 + log6 18 = log6 216 = 3

log2 32 = log2 4 + log2 8 = 2 + 3 + 5




The Power Rule of Logs

If we have log7 x3 =

log7 (x * x * x) =

log7 x + log7 (x * x) =

log7 x + log7 x + log7 x =

3 (log7 x) - so when we take the log of something that has an exponent we can move the exponent as a multiplier to the front of the expression.

log2 64 =
log2 (4 * 4 * 4)
log2 (43) = 3 (log2 4) = 3 * 2 = 6

logbxn = n logb x

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42x = 6

log (42x) = log(6)
2x log(4) = log(6)
2x = (log(6)/log(4)
x = log(6)/log(4)/2

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2x+3 = 54

log (2x+3) = log(54)
(x+3) log(2) = log(54)
x log(2) + 3 log(2) = log(54)
x log(2) = log(54) - 3 log(2) x = (log(54) - 3 log(2)) / log(2)
x = 2.7548




Exponentail Rule (Inverse of the log)

log4 (x -1 ) = 3
4log4(x-1) = 43
x-1 = 64
x = 65


log(x+2) = 4
10log(x+2) = 104
x + 2 = 10000
x = 9998





Logarithm Quotient Rule

log(30x) - log(6) = 4
log(30x/6) = 4
log(5x) = 4
10log(5x) = 104 // exponental rule
5x = 10000
x = 2000

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log5 25 - log5 5 =
log5 (25/5) =
log5 (5) = 1