### All GMAT Math Resources

## Example Questions

### Example Question #1 : How To Graph A Logarithm

What is the -intercept of the graph of ?

**Possible Answers:**

The graph has no -intercept.

**Correct answer:**

Set and solve:

The -intercept is .

### Example Question #2 : How To Graph A Logarithm

What is the -intercept of the graph of ?

**Possible Answers:**

The graph has no -intercept.

**Correct answer:**

Set and evaluate :

Since ,

, and the -intercept is .

### Example Question #3 : How To Graph A Logarithm

What is the vertical asymptote of the graph of ?

**Possible Answers:**

The graph has no vertical asymptote.

**Correct answer:**

The graph of a logarithmic function has a vertical asymptote which can be found by finding the value at which the power is equal to 0:

If , then is an undefined expression, so the vertical asymptote is .

### Example Question #4 : How To Graph A Logarithm

Define a function as follows:

Give the -intercept of the graph of .

**Possible Answers:**

The graph of has no -intercept.

**Correct answer:**

Set and evaluate to find the -coordinate of the -intercept.

This can be rewritten in exponential form:

The -intercept of the graph of is .

### Example Question #5 : How To Graph A Logarithm

Define a function as follows:

Give the -intercept of the graph of .

**Possible Answers:**

The graph of has no -intercept.

**Correct answer:**

The graph of has no -intercept.

The -coordinate of the -intercept is :

However, the logarithm of a negative number is an undefined expression, so is an undefined quantity, and the graph of has no -intercept.

### Example Question #6 : How To Graph A Logarithm

Define a function as follows:

Give the equation of the vertical asymptote of the graph of .

**Possible Answers:**

**Correct answer:**

Only positive numbers have logarithms, so

The graph never crosses the vertical line of the equation , so this is the vertical asymptote.

### Example Question #7 : How To Graph A Logarithm

Define a function as follows:

Give the equation of the vertical asymptote of the graph of .

**Possible Answers:**

The graph of has no vertical asymptote.

**Correct answer:**

Only positive numbers have logarithms, so

The graph never crosses the vertical line of the equation , so this is the vertical asymptote.

### Example Question #8 : How To Graph A Logarithm

Define a function as follows:

Give the -intercept of the graph of .

**Possible Answers:**

The graph of has no -intercept.

**Correct answer:**

The -coordinate of the -intercept is :

Since 2 is the cube root of 8, , and . Therefore,

.

The -intercept is .

### Example Question #9 : How To Graph A Logarithm

Define functions and as follows:

Give the -coordinate of a point at which the graphs of the functions intersect.

**Possible Answers:**

The graphs of and do not intersect.

**Correct answer:**

Since , the definition of can be rewritten as follows:

First, we need to find the -coordinate of the point at which the graphs of and meet by setting

Since the common logarithms of the polynomial and the rational expression are equal, we can set those expressions themselves equal, then solve:

We can solve using the method, finding two integers whose sum is 24 and whose product is - these integers are 10 and 14, so we split the niddle term, group, and factor:

or

This gives us two possible -coordinates. However, since

,

an undefined quantity - negative numbers not having logarithms -

we throw this value out. As for the other -value, we evaluate:

and

is the correct -value, and is the correct -value.

### Example Question #10 : How To Graph A Logarithm

Let be the point of intersection of the graphs of these two equations:

Evaluate .

**Possible Answers:**

**Correct answer:**

Substitute and for and , respectively, and solve the resulting system of linear equations:

Multiply the first equation by 2, and the second by 3, on both sides, then add:

Now back-solve:

We need to find both and to ensure a solution exists. By substituting back:

.

is the solution, and , the correct choice.

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