Precalculus : Pre-Calculus

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Find Intercepts And Asymptotes

Suppose the function below has an oblique (i.e. slant asymptote) at \(\displaystyle y=3x\).

\(\displaystyle \frac{ax^n+3x+5}{bx^m+6}\)

If we are given \(\displaystyle n>2\), what can we say about the relation between \(\displaystyle n\) and \(\displaystyle m\) and between \(\displaystyle a\) and \(\displaystyle b\)?

Possible Answers:

\(\displaystyle n = m+1\, \textup{and} \, \frac{b}{a}=3\)

\(\displaystyle n = m-1\, \textup{and} \, \frac{b}{a}=3\)

\(\displaystyle n = m+1\, \textup{and} \, \frac{a}{b}=3\)

\(\displaystyle n = m\, \textup{and} \, \frac{b}{a}=3\)

\(\displaystyle n = m-1\, \textup{and} \, \frac{a}{b}=3\)

Correct answer:

\(\displaystyle n = m+1\, \textup{and} \, \frac{a}{b}=3\)

Explanation:

We can only have an oblique asymptote if the degree of the numerator is one more than the degree of the denominator.  This stipulates that \(\displaystyle n\) must equal \(\displaystyle m+1\).  

The slope of the asymptote is determined by the ratio of the leading terms, which means the ratio of \(\displaystyle a\) to \(\displaystyle b\) must be 3 to 1.  The actual numbers are not important.

Finally, since the value of \(\displaystyle n\) is at least three, we know there is no intercept to our oblique asymptote.

Example Question #2 : Find Intercepts And Asymptotes

Find the \(\displaystyle y\)-intercept and asymptote, if possible.  

\(\displaystyle y=\frac{x^2+4x+3}{(x+3)}\)

Possible Answers:

\(\displaystyle \textup{Y-intercept at: } y=1; \textup{ No asymptotes.}\)

\(\displaystyle \textup{Y-intercept at: } y=1; \textup{ Asymptote at: }x=-3\)

\(\displaystyle \textup{Y-intercept at: } y=3; \textup{ Asymptote at: }x=-3\)

\(\displaystyle \textup{Y-intercept at: } y=3; \textup{ No asymptotes.}\)

\(\displaystyle \textup{Y-intercept at: } y=1; \textup{ Asymptote at: }x=3\)

Correct answer:

\(\displaystyle \textup{Y-intercept at: } y=1; \textup{ No asymptotes.}\)

Explanation:

To find the y-intercept of \(\displaystyle y=\frac{x^2+4x+3}{(x+3)}\), simply substitute \(\displaystyle x=0\) and solve for \(\displaystyle y\).

\(\displaystyle y=\frac{0^2+4(0)+3}{(0+3)}=\frac{3}{3}=1\)

The y-intercept is 1.

The numerator, \(\displaystyle x^2+4x+3\), can be simplified by factoring it into two binomials.

\(\displaystyle x^2+4x+3=(x+3)(x+1)\)

\(\displaystyle y=\frac{x^2+4x+3}{(x+3)}=\frac{(x+3)(x+1)}{(x+3)} = x+1\)

There is a removable discontinuity at \(\displaystyle x=-3\), but there are no asymptotes at \(\displaystyle x=-3\) since the \(\displaystyle x+3\) terms can be canceled.

The correct answer is:  \(\displaystyle \textup{Y-intercept at: } y=1; \textup{ No asymptotes.}\)

Example Question #3 : Find Intercepts And Asymptotes

Find the \(\displaystyle \small x\)-intercepts of the rational function

\(\displaystyle \small \frac{2x^2-6x+4}{2x^2+x-1}\).

 

Possible Answers:

\(\displaystyle x=6,-2\)

\(\displaystyle \small x=2,-1\)

\(\displaystyle \small x=1\)

\(\displaystyle \small x=1/2,-1\)

\(\displaystyle \small x=1,2\)

Correct answer:

\(\displaystyle \small x=1,2\)

Explanation:

The \(\displaystyle \small x\)-intercept(s) is/are the root(s) of the numerator of the rational functions.

In this case, the numerator is \(\displaystyle \small 2x^2-6x+4\).

Using the quadratic formula,

\(\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\)

\(\displaystyle x=\frac{6\pm\sqrt{(-6)^2-4(2)(4)}}{2(2)}\)

\(\displaystyle x=\frac{6\pm\sqrt{36-32}}{4}\)

\(\displaystyle x=\frac{6\pm2}{4}=1,2\)

the roots are \(\displaystyle \small x=1,2\).

Thus, \(\displaystyle \small x=1,2\) are the \(\displaystyle \small x\)-intercepts.

Example Question #1 : Find Intercepts And Asymptotes

Find the vertical asymptotes of the following rational function.

\(\displaystyle \small \frac{8x^2}{4x^2+31x-8}\)

Possible Answers:

\(\displaystyle \small x=4,\frac{1}{8}\)

\(\displaystyle \small x=-\frac{1}{8},4\)

\(\displaystyle \small \small x=-\frac{1}{4},8\)

\(\displaystyle \small x=\frac{1}{4}, -8\)

No vertical asymptotes.

Correct answer:

\(\displaystyle \small x=\frac{1}{4}, -8\)

Explanation:

Finding the vertical asymptotes of the rational function \(\displaystyle \small \frac{8x^2}{4x^2+31x-8}\) amounts to finding the roots of the denominator, \(\displaystyle \small 4x^2+31x-8\).

It is easy to check, using the quadratic formula,

\(\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}\)

\(\displaystyle x=\frac{-31\pm\sqrt {31^2-4(4)(-8)}}{2(4)}\)

\(\displaystyle x=\frac{-31\pm\sqrt {961+128}}{8}\)

\(\displaystyle x=\frac{-31\pm 33}{8}=\frac{1}{4}, -8\)

that the roots, and thus the asymptotes, are \(\displaystyle \small x=\frac{1}{4}, -8\).

Example Question #1 : Find Intercepts And Asymptotes

Find the y-intercept and asymptote, respectively, of the following function, if possible.  \(\displaystyle y=\frac{3x}{x}\)

Possible Answers:

\(\displaystyle \textup{y-intercept at: }(0,3);\:\textup{Asymptote at: }x=0\)

\(\displaystyle \textup{y-intercept at: }(0,3);\:\textup{Asymptote at: }y=3\)

\(\displaystyle \textup{There are no y-intercepts or asymptotes.}\)

\(\displaystyle \textup{The y-intercept does not exist. Asymptote at: }x=0\)

\(\displaystyle \textup{y-intercept at: }(0,3);\:\textup{Asymptote at: }y=0\)

Correct answer:

\(\displaystyle \textup{There are no y-intercepts or asymptotes.}\)

Explanation:

Before we start to simplify the problem, it is crucial to immediately identify the domain of this function \(\displaystyle y=\frac{3x}{x}\).

The denominator cannot be zero, since it is undefined to divide numbers by this value.  After simplification, the equation is:

\(\displaystyle y=3\)

The domain is \(\displaystyle x\neq0\) and there is a hole at \(\displaystyle x=0\) since there is a removable discontinuity.  There are no asymptotes.  

Since it's not possible to substitute \(\displaystyle x=0\) into the original equation, the y-intercept also does not exist.

Therefore, the correct answer is:

\(\displaystyle \textup{There are no y-intercepts or asymptotes.}\)

Example Question #6 : Find Intercepts And Asymptotes

What is a vertical asymptote of the following function? 

\(\displaystyle \frac{x^2 + 3x + 6}{x + 2}\)

Possible Answers:

\(\displaystyle y = 3\)

\(\displaystyle y = 2\)

\(\displaystyle x = 3\)

\(\displaystyle x = -3\)

\(\displaystyle x = -2\)

Correct answer:

\(\displaystyle x = -2\)

Explanation:

To find the vertical asymptote of a function, we set the denominator equal to \(\displaystyle 0\)

With our function, we complete this process. 

The denominator is \(\displaystyle x + 2\), so we begin: 

\(\displaystyle x + 2 = 0\)

\(\displaystyle x = -2\)

Example Question #51 : Polynomial Functions

What is the \(\displaystyle y\)-intercept of the following function? 

\(\displaystyle \frac{x^2 + 3x + 6}{x + 2}\)

Possible Answers:

\(\displaystyle -2\)

\(\displaystyle 3\)

There is no \(\displaystyle y\)-intercept. 

\(\displaystyle 6\)

\(\displaystyle 2\)

Correct answer:

\(\displaystyle 3\)

Explanation:

The y-intercept of a function is always found by substituting in \(\displaystyle x = 0\).

We can go through this process for our function. 

\(\displaystyle \frac{x^2 + 3x + 6}{x + 2}= \frac{0^2 + 3\cdot 0+ 6}{0 + 2} = \frac{ 6}{ 2} = 3\)

Example Question #8 : Find Intercepts And Asymptotes

Which of these functions has a vertical asymptote of \(\displaystyle x = 3\) and a slant asymptote of \(\displaystyle y = x - 8\)?

Possible Answers:

\(\displaystyle y = \frac{x^2 - 11x + 24}{x - 3 }\)

\(\displaystyle y = \frac{x^2 + 11x + 9 }{x - 3 }\)

\(\displaystyle y = \frac{x^2 - 11x + 7 }{ x - 3 }\)

\(\displaystyle y = \frac{x^2 + 11x - 7 }{x + 3 }\)

\(\displaystyle y = \frac{x^2 - 11x + 9 }{x + 3 }\)

Correct answer:

\(\displaystyle y = \frac{x^2 - 11x + 7 }{ x - 3 }\)

Explanation:

In order for the vertical asymptote to be \(\displaystyle x = 3\), we need the denominator to be \(\displaystyle x -3\). This gives us three choices of numerators:

\(\displaystyle x^2 - 11x + 24\)

\(\displaystyle x^2 - 11x + 7\)

\(\displaystyle x^2 + 11x + 9\)

If the slant asymptote is \(\displaystyle x - 8\), we will be able to divide our numerator by \(\displaystyle x - 3\) and get \(\displaystyle x - 8\) with a remainder.

Dividing the first one gives us \(\displaystyle x - 8\) with no remainder.

Dividing the last one gives us \(\displaystyle x + 14\) with a remainder.

The middle numerator would give us what we were after, \(\displaystyle x - 8\) with a remainder of -17.

The answer is

\(\displaystyle y = \frac{x^2 - 11x + 7 }{ x - 3 }\)

Example Question #9 : Find Intercepts And Asymptotes

Find the zeros and asymptotes for

\(\displaystyle y = \frac{2x^2 + 5 x - 3 }{2x^2 + 3x - 2 }\).

Possible Answers:

Zero: \(\displaystyle x = -3\); Asymptotes: \(\displaystyle x = -2, \frac{1}{2}\)

Zeros: \(\displaystyle x = 2, \frac{1}{2}\); Asymptotes: \(\displaystyle x = 3, \frac{1}{2}\)

Zero: \(\displaystyle x = -3\); Asymptote: \(\displaystyle x = -2\)

Zeros: \(\displaystyle x = 3, -1\); Asymptote: \(\displaystyle x = 2\)

Zero: \(\displaystyle x = \frac{1}{2}\); Asymptotes: \(\displaystyle x = 2, -\frac{1}{2}\)

Correct answer:

Zero: \(\displaystyle x = -3\); Asymptote: \(\displaystyle x = -2\)

Explanation:

To find the information we're looking for, we should factor this equation:

\(\displaystyle y = \frac{(2 x - 1 )(x + 3 )}{(2 x - 1 )(x+ 2 )}\)

This means that it simplifies to \(\displaystyle y = \frac{x + 3 }{ x + 2 }\).

When the equation is in the form of a fraction, to find the zero of the function we need to set the numerator equal to zero and solve for the variable.

\(\displaystyle \\x+3=0\\x=-3\)

To find the asymptote of an equation with a fraction we need to set the denominator of the fraction equal to zero and solve for the variable.

\(\displaystyle \\x+2=0\\x=-2\)

Therefore our equation has a zero at -3 and an asymptote at -2.

Example Question #10 : Find Intercepts And Asymptotes

Find the slant and vertical asymptotes for the equation

\(\displaystyle y = \frac{2x^2 - 5 x + 1 }{x + 3 }\).

Possible Answers:

Vertical asymptote: \(\displaystyle x = -3\); Slant asymptote: \(\displaystyle y = 2 x + 1\)

Vertical asymptote: \(\displaystyle x = -3\); Slant asymptote: \(\displaystyle y = 2x^2 - 11 x + 34\)

Vertical asymptote: \(\displaystyle x = -3\); Slant asymptote: \(\displaystyle y = 2x -1\)

Vertical asymptote: \(\displaystyle x = -3\); Slant asymptote: \(\displaystyle y = 2x - 8\)

Vertical asymptote: \(\displaystyle x = 3\); Slant asymptote: \(\displaystyle y = 2x + 1\)

Correct answer:

Vertical asymptote: \(\displaystyle x = -3\); Slant asymptote: \(\displaystyle y = 2x - 8\)

Explanation:

To find the vertical asymptote, just set the denominator equal to 0:

\(\displaystyle x + 3 = 0\)

\(\displaystyle x = -3\)

To find the slant asymptote, divide the numerator by the denominator, but ignore any remainder. You can use long division or synthetic division.

               \(\displaystyle 2x-8\)

\(\displaystyle \\x+3\ |\overline{2 x^ 2 - 5 x + 1 }\)

          \(\displaystyle \\ \underline{-(2x^2+3x) }\)

                         \(\displaystyle -8x+1\)

                   \(\displaystyle \underline{-(-8x-24)}\)

                                       \(\displaystyle 25\)

The slant asymptote is

\(\displaystyle y = 2x - 8\).

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