Precalculus : Hyperbolas and Ellipses

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #71 : Understand Features Of Hyperbolas And Ellipses

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle 9x^2-4y^2-162x-8y+689=0

Possible Answers:

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

\displaystyle y=-\frac{2}{3}x-2

\displaystyle y=\frac{1}{9}x-2

\displaystyle y=-\frac{1}{9}x+\frac{16}{9}

\displaystyle y=\frac{3}{2}x-\frac{29}{2}

\displaystyle y=-\frac{3}{2}x-\frac{25}{2}

\displaystyle y=\frac{9}{4}x-\frac{14}{4}

\displaystyle y=-\frac{9}{4}x+\frac{3}{4}

Correct answer:

\displaystyle y=\frac{3}{2}x-\frac{29}{2}

\displaystyle y=-\frac{3}{2}x-\frac{25}{2}

Explanation:

For a hyperbola with its foci on the \displaystyle x-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(x-h)^2}{a^2}-\frac{(y-k)^2}{b^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

Start by putting the given equation into the standard form of the equation of a hyperbola.

Group the \displaystyle x terms together and \displaystyle y terms together.

\displaystyle 9x^2-4y^2-162x-8y+689=0

\displaystyle 9x^2-162x-4y^2-8y+689=0

Factor out \displaystyle 9 from the \displaystyle x terms and \displaystyle -4 from the \displaystyle y terms.

\displaystyle 9(x^2-18x)-4(y^2+2y)+689=0

Complete the squares. Remember to add the amount amount to both sides of the equation!

\displaystyle 9(x^2-18x+81)-4(y^2+2y+1)+689=725

Subtract \displaystyle 689 from both sides of the equation:

\displaystyle 9(x^2-18x+81)-4(y^2+2y+1)=36

Divide both sides by \displaystyle 36.

\displaystyle \frac{x^2-18x+81}{4}-\frac{y^2+2y+1}{9}=1

Factor the two terms to get the standard form of the equation of a hyperbola.

\displaystyle \frac{(x-9)^2}{4}-\frac{(y+1)^2}{9}=1

The slopes of the asymptotes for this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=2 and \displaystyle b=3.

Thus, the slopes for its asymptotes are \displaystyle m=\pm\frac{3}{2}.

Plug in the center of the hyperbola into the point-slope form of a line to find the equations of the asymptotes. The center of the hyperbola is \displaystyle (9, -1).

\displaystyle y+1=\pm\frac{3}{2}(x-9)

Now, simplify each equation. For the first equation,

\displaystyle y+1=\frac{3}{2}(x-9)

\displaystyle y+1=\frac{3}{2}x-\frac{27}{2}

\displaystyle y=\frac{3}{2}x-\frac{29}{2}

For the second equation,

\displaystyle y+1=-\frac{3}{2}(x-9)

\displaystyle y+1=-\frac{3}{2}x+\frac{27}{2}

\displaystyle y=-\frac{3}{2}x-\frac{25}{2}

Example Question #1744 : Pre Calculus

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle \frac{(x-12)^2}{144}-\frac{(y+\sqrt3)^2}{169}=1

Possible Answers:

\displaystyle y=\pm\frac{12}{13}(x+\sqrt3)+12

\displaystyle y=\pm\frac{144}{169}(x-12)-\sqrt3

\displaystyle y=\pm\frac{13}{12}(x-12)+\sqrt3

\displaystyle y=\pm\frac{169}{144}(x+12)-\sqrt3

Correct answer:

\displaystyle y=\pm\frac{13}{12}(x-12)+\sqrt3

Explanation:

For a hyperbola with its foci on the \displaystyle x-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(x-h)^2}{a^2}-\frac{(y-k)^2}{b^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

The slopes of the asymptotes for this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=12 and \displaystyle b=13.

Thus, the slopes for its asymptotes are \displaystyle m=\pm\frac{13}{12}

Now, plug in the coordinates for the center of the hyperbola \displaystyle (12, \sqrt3) into the point-slope form of the line to find the equations of the asymptotes.

\displaystyle y-\sqrt3=\pm\frac{13}{12}(x-12)

\displaystyle y=\pm\frac{13}{12}(x-12)+\sqrt3

Example Question #1742 : Pre Calculus

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle \frac{(x-2)^2}{100}-\frac{(y-6)^2}{36}=1

Possible Answers:

\displaystyle y=\frac{3}{5}x+\frac{24}{5}

\displaystyle y=-\frac{3}{5}x+\frac{36}{5}

\displaystyle y=\frac{5}{3}x-\frac{7}{3}

\displaystyle y=-\frac{5}{3}x+\frac{8}{3}

\displaystyle y=\frac{25}{9}x-\frac{8}{9}

\displaystyle y=-\frac{25}{9}x+\frac{2}{3}

\displaystyle y=\frac{9}{25}x-\frac{1}{5}

\displaystyle y=-\frac{9}{25}x+\frac{9}{5}

Correct answer:

\displaystyle y=\frac{3}{5}x+\frac{24}{5}

\displaystyle y=-\frac{3}{5}x+\frac{36}{5}

Explanation:

For a hyperbola with its foci on the \displaystyle x-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(x-h)^2}{a^2}-\frac{(y-k)^2}{b^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

The slopes of the asymptotes for this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle 10 and \displaystyle b=6.

Thus, the slopes for its asymptotes are \displaystyle m=\pm\frac{6}{10}=\pm\frac{3}{5}.

Now, use the point-slope form of a line in addition to the center of the hyperbola to find the equations of the asymptotes.

The center is at \displaystyle (2, 6).

The first equation of the asymptote would be the following:

\displaystyle y-6=\frac{3}{5}(x-2)

\displaystyle y-6=\frac{3}{5}x-\frac{6}{5}

\displaystyle y=\frac{3}{5}x+\frac{24}{5}

The second equation of the asymptote would be the following:

\displaystyle y-6=-\frac{3}{5}(x-2)

\displaystyle y-6=-\frac{3}{5}x+\frac{6}{5}

\displaystyle y=-\frac{3}{5}+\frac{36}{5}

 

Example Question #1745 : Pre Calculus

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle \frac{y^2}{9}-\frac{x^2}{25}=1

Possible Answers:

\displaystyle y=\pm\frac{3}{5}x

\displaystyle y=\pm\frac{9}{25}x

\displaystyle y=\pm\frac{25}{9}x

\displaystyle y=\pm\frac{5}{3}x

Correct answer:

\displaystyle y=\pm\frac{3}{5}x

Explanation:

For a hyperbola with its foci on the \displaystyle y-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(y-k)^2}{b^2}-\frac{(x-h)^2}{a^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

The slopes of the asymptotes for this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=5 and \displaystyle b=3.

Since the center is \displaystyle (0, 0), the equations for its asymptotes are \displaystyle y=\pm\frac{3}{5}x.

Example Question #1744 : Pre Calculus

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle \frac{(y-9)^2}{169}-\frac{(x-2)^2}{225}=1

Possible Answers:

\displaystyle y=2x-9

\displaystyle y=-2x+8

\displaystyle y=\frac{15}{13}x-\frac{20}{13}

\displaystyle y=-\frac{15}{13}x+\frac{5}{13}

\displaystyle y=\frac{13}{15}x+\frac{109}{15}

\displaystyle y=-\frac{13}{15}x+\frac{161}{15}

\displaystyle y=\frac{2}{9}x-\frac{7}{2}

\displaystyle y=-\frac{2}{9}x+\frac{25}{2}

Correct answer:

\displaystyle y=\frac{13}{15}x+\frac{109}{15}

\displaystyle y=-\frac{13}{15}x+\frac{161}{15}

Explanation:

For a hyperbola with its foci on the \displaystyle y-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(y-k)^2}{b^2}-\frac{(x-h)^2}{a^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

The slopes of the asymptotes for this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=15 and \displaystyle b=13.

Thus, the slopes for its asymptotes are \displaystyle \pm\frac{13}{15}.

Now, plug in the center of the hyperbola, \displaystyle (2, 9) into the point-slope form of a line to find the equations of the asymptotes.

For the first asymptote, 

\displaystyle y-9=\frac{13}{15}(x-2)

\displaystyle y-9=\frac{13}{15}x-\frac{26}{15}

\displaystyle y=\frac{13}{15}x+\frac{109}{15}

For the second asymptote,

\displaystyle y-9=-\frac{13}{15}(x-2)

\displaystyle y-9=-\frac{13}{15}x+\frac{26}{15}

\displaystyle y=-\frac{13}{15}x+\frac{161}{15}

Example Question #1745 : Pre Calculus

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle \frac{(y-1)^2}{8}-\frac{(x+2)^2}{36}=1

Possible Answers:

\displaystyle y=\pm\frac{3\sqrt2}{2}(x-2)-1

\displaystyle y=\pm\frac{\sqrt2}{3}(x+2)+1

\displaystyle y=\pm\frac{1}{8}(x-2)-1

\displaystyle y=\pm\frac{2\sqrt2}{3}(x-1)+9

Correct answer:

\displaystyle y=\pm\frac{\sqrt2}{3}(x+2)+1

Explanation:

For a hyperbola with its foci on the \displaystyle y-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(y-k)^2}{b^2}-\frac{(x-h)^2}{a^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

The slopes of this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=6 and \displaystyle b=\sqrt8=2\sqrt2.

Thus, the slopes for its asymptotes are \displaystyle \pm\frac{2\sqrt2}{6}=\pm\frac{\sqrt2}{3}.

Now, plug in the center of the hyperbola into the point-slope form of the equation fo the line to get the equations of the asymptotes.

The center of the hyperbola is \displaystyle (-2, 1). The equations of the asymptotes are then:

\displaystyle y-1=\pm\frac{\sqrt2}{3}(x+2)

\displaystyle y=\pm\frac{\sqrt2}{3}(x+2)+1

Example Question #71 : Understand Features Of Hyperbolas And Ellipses

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle \frac{(y-4)^2}{196}-\frac{(x+\pi)^2}{400}=1

Possible Answers:

\displaystyle y=\pm\frac{13}{20}(x-\pi)+8

\displaystyle y=\pm\frac{20}{13}(x+4)+\pi

\displaystyle y=\pm\frac{13}{20}(x+\pi)+4

\displaystyle y=\pm\frac{\pi}{4}(x-2)+1

Correct answer:

\displaystyle y=\pm\frac{13}{20}(x+\pi)+4

Explanation:

For a hyperbola with its foci on the \displaystyle y-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(y-k)^2}{b^2}-\frac{(x-h)^2}{a^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

The slopes of this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=20 and \displaystyle b=13.

Thus, the slopes for its asymptotes are \displaystyle \pm\frac{13}{20}.

Now, plug in the center of the hyperbola into the point-slope form of an equation of a line to find the equations of the asymptotes. The center of the hyperbola is \displaystyle (-\pi, 4).

The equations of the asymptotes can be then given by the following:

\displaystyle y-4=\pm\frac{13}{20}(x+\pi)

\displaystyle y=\pm\frac{13}{20}(x+\pi)+4

Example Question #72 : Understand Features Of Hyperbolas And Ellipses

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle 36y^2-16x^2-144y-32x-448=0

Possible Answers:

\displaystyle y=\frac{2}{3}x+\frac{8}{3}

\displaystyle y=-\frac{2}{3}x+\frac{4}{3}

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

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

\displaystyle y=\pm\frac{4}{3}x

\displaystyle y=\frac{3}{2}x+3

\displaystyle y=-\frac{3}{2}x-\frac{5}{2}

Correct answer:

\displaystyle y=\frac{2}{3}x+\frac{8}{3}

\displaystyle y=-\frac{2}{3}x+\frac{4}{3}

Explanation:

For a hyperbola with its foci on the \displaystyle y-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(y-k)^2}{b^2}-\frac{(x-h)^2}{a^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

Start by putting the given equation into the standard form of the equation of a hyperbola.

Group the \displaystyle x terms together and \displaystyle y terms together.

\displaystyle 36y^2-16x^2-144y-32x-448=0

\displaystyle 36y^2-144y-16x^2-32x-448=0

Factor out \displaystyle -16 from the \displaystyle x terms and \displaystyle 36 from the \displaystyle y terms.

\displaystyle 36(y^2-4y)-16(x^2+2x)-448=0

Complete the squares. Remember to add the amount amount to both sides of the equation!

\displaystyle 36(y^2-4y+4)-16(x^2+2x+1)-448=98

Add \displaystyle 448 to both sides of the equation:

\displaystyle 36(y^2-4y+4)-16(x^2+2x+1)=576

Divide both sides by \displaystyle 576.

\displaystyle \frac{y^2-4y+4}{16}-\frac{x^2+2x+1}{36}=1

Factor the two terms to get the standard form of the equation of a hyperbola.

\displaystyle \frac{(y-2)^2}{16}-\frac{(x+1)^2}{36}=1

The slopes of this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=6 and \displaystyle b=4.

Thus, the slopes for its asymptotes are \displaystyle \pm\frac{4}{6}=\pm\frac{2}{3}.

Now, plug in the center of the hyperbola, \displaystyle (-1, 2) into the point-slope form of the equation of a line to get the equations of the asymptotes.

For the first equation, 

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

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

\displaystyle y=\frac{2}{3}x+\frac{8}{3}

For the second equation,

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

\displaystyle y-2=-\frac{2}{3}x-\frac{2}{3}

\displaystyle y=-\frac{2}{3}x+\frac{4}{3}

Example Question #78 : Understand Features Of Hyperbolas And Ellipses

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle 4y^2-54x^2-24y+108x-234=0

Possible Answers:

\displaystyle y=\pm\frac{4\sqrt3}{2}(x+3)-1

\displaystyle y=\pm\frac{1}{3}x

\displaystyle y=\pm\frac{2\sqrt6}{3}(x-1)+3

\displaystyle y=\pm\frac{3\sqrt6}{2}(x-1)+3

Correct answer:

\displaystyle y=\pm\frac{3\sqrt6}{2}(x-1)+3

Explanation:

For a hyperbola with its foci on the \displaystyle y-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(y-k)^2}{b^2}-\frac{(x-h)^2}{a^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

Start by putting the given equation into the standard form of the equation of a hyperbola.

Group the \displaystyle x terms together and \displaystyle y terms together.

\displaystyle 4y^2-54x^2-24y+108x-234=0

\displaystyle 4y^2-24y-54x^2+108x-234=0

Factor out \displaystyle -54 from the \displaystyle x terms and \displaystyle 4 from the \displaystyle y terms.

\displaystyle 4(y^2-6y)-54(x^2-2x)-234=0

Complete the squares. Remember to add the amount amount to both sides of the equation!

\displaystyle 4(y^2-6y+9)-54(x^2-2x+1)-234=-18

Add \displaystyle 234 to both sides of the equation:

\displaystyle 4(y^2-6y+9)-54(x^2-2x+1)=216

Divide both sides by \displaystyle 216.

\displaystyle \frac{y^2-6y+9}{54}-\frac{x^2-2x+1}{4}=1

Factor the two terms to get the standard form of the equation of a hyperbola.

\displaystyle \frac{(y-3)^2}{54}-\frac{(x-1)^2}{4}=1

The slopes of this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=2 and \displaystyle b=\sqrt{54}=3\sqrt6.

Thus, the slopes for its asymptotes are \displaystyle \pm\frac{3\sqrt6}{2}.

Now, plug in the center of the hyperbola into the point-slope form of the equation of alien to get the equations for the asymptotes.

The center of the hyperbola is \displaystyle (1, 3).

The equations for the asymptotes are then:

\displaystyle y-3=\pm\frac{3\sqrt6}{2}(x-1)

\displaystyle y=\pm\frac{3\sqrt6}{2}(x-1)+3

 

Example Question #72 : Hyperbolas And Ellipses

Find the equations of the asymptotes for the hyperbola with the following equation:

\displaystyle \frac{(x-5)^2}{24}-\frac{(y+3)^2}{25}=1

Possible Answers:

\displaystyle y=\pm\frac{5}{24}(x-5)-3

\displaystyle y=\pm\frac{5\sqrt6}{12}(x-5)-3

\displaystyle y=\pm\frac{12\sqrt6}{25}(x-5)+3

\displaystyle y=\pm\frac{24}{25}(x+5)+3

Correct answer:

\displaystyle y=\pm\frac{5\sqrt6}{12}(x-5)-3

Explanation:

For a hyperbola with its foci on the \displaystyle x-axis, like the one given in the equation, recall the standard form of the equation:

\displaystyle \frac{(x-h)^2}{a^2}-\frac{(y-k)^2}{b^2}=1, where \displaystyle (h,k) is the center of the hyperbola.

The slopes of the asymptotes for this hyperbola are given by the following:

\displaystyle m=\pm\frac{b}{a}

For the hyperbola in question, \displaystyle a=\sqrt{24}=2\sqrt6 and \displaystyle b=5.

Thus, the slopes for its asymptotes are \displaystyle m=\pm\frac{5}{2\sqrt6}=\pm\frac{5\sqrt6}{12}.

Now, use the point-slope form of a line in addition to the center of the hyperbola to find the equations of the asymptotes.

The center is at \displaystyle (5,-3).

To find the equations of the asymptotes, use the point-slope form of a line.

\displaystyle y+3=\pm\frac{5\sqrt6}{12}(x-5)

\displaystyle y=\frac{5\sqrt6}{12}(x-5)-3

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