Advanced Geometry : How to graph a logarithm

Study concepts, example questions & explanations for Advanced Geometry

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Example Questions

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Example Question #1 :Coordinate Geometry

What is the-intercept of the graph of?

Possible Answers:

The graph has no-intercept.

Correct answer:

Explanation:

Setand 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:

Explanation:

Setand 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:

Explanation:

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, thenis an undefined expression, so the vertical asymptote is.

Example Question #4 :How To Graph A Logarithm

Define a functionas follows:

Give the-intercept of the graph of.

Possible Answers:

The graph ofhas no-intercept.

Correct answer:

Explanation:

Setand evaluateto find the-coordinate of the-intercept.

This can be rewritten in exponential form:

The-intercept of the graph ofis.

Example Question #5 :How To Graph A Logarithm

Define a functionas follows:

Give the-intercept of the graph of.

Possible Answers:

The graph ofhas no-intercept.

Correct answer:

The graph ofhas no-intercept.

Explanation:

The-coordinate of the-intercept is:

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

Example Question #6 :How To Graph A Logarithm

Define a functionas follows:

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

Possible Answers:

Correct answer:

Explanation:

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 functionas follows:

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

Possible Answers:

The graph ofhas no vertical asymptote.

Correct answer:

Explanation:

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 functionas follows:

Give the-intercept of the graph of.

Possible Answers:

The graph ofhas no-intercept.

Correct answer:

Explanation:

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 functionsandas follows:

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

Possible Answers:

The graphs ofanddo not intersect.

Correct answer:

Explanation:

Since, the definition ofcan be rewritten as follows:

First, we need to find the-coordinate of the point at which the graphs ofandmeet 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 themethod, 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, andis the correct-value.

Example Question #10 :How To Graph A Logarithm

Letbe the point of intersection of the graphs of these two equations:

Evaluate.

Possible Answers:

Correct answer:

Explanation:

Substituteandforand, 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 bothandto ensure a solution exists. By substituting back:

.

is the solution, and, the correct choice.

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