Facts of exponents:
bu+v ↔ bu·bv
Exs:
23+4 = 23·24
x3+4 = x3·x4
2x+y = 2x·2y
bu-v ↔ bu / bv
Exs:
27-4 = 27 / 24
x7-4 = x7 / x4
2x-y = 2x / 2y
(bu)v ↔ buv
Exs:
(23)4 = 23·4
(x3)4 = x3·4
(2x)y = 2x·y
Facts of logarithms: for every base
log uv ↔ log u + log v
Exs:
log 3x = log 3 + log x
log u/v ↔ log u - logv
Exs:
log 3/x = log 3 - log x
log uv ↔ v·log u
Exs:
log 3x = x log 3
log x3 = 3 log x
→ expand, split
← reassemble, combine, compactify
If both sides are exponential and the bases are the same or can be rewritten as the same base:
Use: blhs = brhs → lhs = rhs
Ex. 4x = 23 Rewrite: (22)x=22x = 23, 2x=3, x=3/2
Equations:
lhs = rhs ↔ blhs = brhs
Raise both sides of equation as exponents of some base b or set the exponents as equal.
lhs = rhs ↔ logblhs = logbrhs
Take logs of both sides of equation or set the logs' arguments as equal.
Solve equation for variable x:
If x is in exponent in equation i.e. bx, take logb of each side
of the equation to get the x out of exponent (the log will "undo" the exponent):
logbbx → = x
(the exponent to raise b to to get bx is x),
Inverse functions: log(exp(x))=x
Ex.
5x = 100
log5 5x = log5 100
x = log5 100
x ≈ 2.86135
Ex.
e2x = 100
ln e2x = ln 100
2x = ln 100
x = (ln 100) / 2
x ≈ 2.30258
If x is in logarithm in equation i.e. logbx, raise the base b to both sides of
the equation i.e. blogbx
to get the x out of log (the exponentiation will "undo" the logarithm):
blogbx → = x
(raise b to the exponent that b has to be raised to to get x is x)
Inverse functions: exp(log(x))=x
Ex.
log52x = 3
5log52x = 53
2x = 125
x = 62.5
Ex.
ln 2x = 3
eln 2x = e3
2x = e3
x ≈ 10.04276