ACT Math › How to find a logarithm
If , then
?
4
5
10
15
25
Calculate the power of that makes the expression equal to 25. We can set up an alternate or equivalent equation to solve this problem:
Solve this equation by taking the square root of both sides.
, because logarithmic equations cannot have a negative base.
The solution to this expression is:
If log4 x = 2, what is the square root of x?
2
3
4
12
16
Given log4_x_ = 2, we can determine that 4 to the second power is x; therefore the square root of x is 4.
Simplify:
Here, we need to make use of some logarithm identities:
Therefore, putting all of those things together, we get the final answer of
How can we simplify this expression below into a single logarithm?
Cannot be simplified into a single logarithm
Using the property that , we can simplify the expression to
.
Given that and
We can further simplify this equation to
Evaluate
log327
9
27
30
3
10
You can change the form to
3_x_ = 27
x = 3
If , what is
?
Use the following equation to easily manipulate all similar logs:
changes to
.
Therefore, changes to
.
2 raised to the power of 6 yields 64, so must equal 6. If finding the 6 was difficult from the formula, simply keep multiplying 2 by itself until you reach 64.
Solve for x in the following equation:
log224 - log23 = log_x_27
3
2
9
**–**2
1
Since the two logarithmic expressions on the left side of the equation have the same base, you can use the quotient rule to re-express them as the following:
log224 – log23 = log2(24/3) = log28 = 3
Therefore we have the following equivalent expressions, from which it can be deduced that x = 3.
log_x_27 = 3
_x_3 = 27
y = 2x
If y = 3, approximately what is x?
Round to 4 decimal places.
0.6309
1.8580
1.3454
1.5850
2.0000
To solve, we use logarithms. We log both sides and get: log3 = log2x
which can be rewritten as log3 = xlog2
Then we solve for x: x = log 3/log 2 = 1.5850 . . .
Solve for
.
Round to the nearest hundredth.
To solve an exponential equation like this, you need to use logarithms. This can be translated into:
Now, remember that your calculator needs to have this translated. The logarithm is equal to the following:
, which equals approximately
.
Remember that you have the equation:
Thus, .
Solve the following equation
.
In order to solve a question like this, you will need to use logarithms. First, start by converting this into a basic logarithm:
Recall that you need to convert for your calculator:
, which equals approximately
Thus, you can solve for :