Precalculus : Conic Sections

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1793 : Pre Calculus

Find the foci for the hyperbola with the following equation:

Possible Answers:

Correct answer:

Explanation:

Recall that the standard formula of a hyperbola can come in two forms:

 and

, where the centers of both hyperbolas are .

When the term with  is first, that means the foci will lie on a horizontal transverse axis.

When the term with  is first, that means the foci will lie on a vertical transverse axis.

To find the foci, we use the following:

For a hyperbola with a horizontal transverse access, the foci will be located at  and .

For a hyperbola with a vertical transverse access, the foci will be located at  and .

For the given hypebola in the question, the transverse axis is vertical and its center is located at .

Next, find .

The foci are then located at  and .

Example Question #1794 : Pre Calculus

Which point is one of the foci of the hyperbola ?

Possible Answers:

Correct answer:

Explanation:

To find the foci of a hyperbola, first determine a and b, and then use the relationship

In this case, the major axis is horizontal since x comes first, so and .

Solve for c: add 9 to both sides 

take the square root

Since the center is and the major axis is the horizontal one, our foci are . The only choice that works is

.

Example Question #121 : Understand Features Of Hyperbolas And Ellipses

Determine the length of the foci for the following hyperbola equation:

Possible Answers:

Correct answer:

Explanation:

To solve, simply use the follow equation where c is the length of the foci.

In this particular case,

Thus,

Example Question #1795 : Pre Calculus

Find the foci of the hyperbola with the following equation:

Possible Answers:

 and 

 and 

 and 

 and 

 and 

Correct answer:

 and 

Explanation:

The standard form of the equation for a hyperbola is given by

The foci are located at (h+c, k) and (h-c, k), where c is found by using the formula

Since our equation is already in standard form, you can see that

Plugging into the formula

So the foci are found at

 AND

 

 

Example Question #1791 : Pre Calculus

How can this graph be changed to be the graph of

?

Wrong hyperbola 1

Possible Answers:

The -intercepts should be at the points and .

The center box should extend up to  and down to , stretching the graph.

The graph should have -intercepts and not -intercepts.

The graph should be an ellipse and not a hyperbola.

The -intercepts should be at the points and .

Correct answer:

The -intercepts should be at the points and .

Explanation:

This equation should be thought of as .

This means that the hyperbola will be determined by a box with x-intercepts at and y-intercepts at .

The hyperbola was incorrectly drawn with the intercepts at instead.

Example Question #211 : Conic Sections

Which of the following would NOT be true of the graph for ?

Possible Answers:

The graph opens up and down.

The graph is centered at .

The graph never intersects with the -axis.

All of these statements are true.

The graph never intersects with the -axis.

Correct answer:

The graph never intersects with the -axis.

Explanation:

The graph should look like this:

Right hyperbola 2

Example Question #1797 : Pre Calculus

Which of these equations produce this graph, rotated 90 degrees?

Wrong hyperbola 1

Possible Answers:

Correct answer:

Explanation:

Rotated 90 degrees, this graph would be opening up and down instead of left and right, so the equation will have the y term minus the x term.

The box that the hyperbola is drawn around will also rotate. It will now be up/down 2 and left/right 3.

This makes the correct equation

.

Example Question #125 : Hyperbolas And Ellipses

What is the equation of the conic section graphed below?Right hyperbola 1

Possible Answers:

Correct answer:

Explanation:

The hyperbola pictured is centered at , meaning that the equation has a horizontal shift. The equation must have rather than just x. The hyperbola opens up and down, so the equation must be the y term minus the x term. The hyperbola is drawn according to the box going up/down 5 and left/right 2, so the y term must be or , and the x term must be  or .

Example Question #1801 : Pre Calculus

The equation of an ellipse, , is . Which of the following is the correct eccentricity of this ellipse?

Possible Answers:

Correct answer:

Explanation:

The equation for the eccentricity of an ellipse is , where  is eccentricity,  is the distance from the foci to the center, and  is the square root of the larger of our two denominators.

Our denominators are  and , so .

To find , we must use the equation , where  is the square root of the smaller of our two denominators.

This gives us , so .

Therefore, we can see that

 .

Example Question #1 : Determine The Equation Of A Parabola And Graph A Parabola

Determine the direction in which the following parabola opens, if the y-axis is vertical and the x-axis is horizontal:

Possible Answers:

Left

Right

Up

Down

Along 

Correct answer:

Left

Explanation:

In order to determine which direction the parabola opens, we must first put the equation in standard form, which can be expressed in one of the following two ways:

If the equation is for  as in the first above, the parabola opens up if  is positive and down if is negative. If the equation is for as in the second above, the parabola opens right if is positive and left if is negative. Rearranging our equation, we get:

We can see that our equation is for , which means the parabola will open either left or right. The sign of the first term is negative, so this parabola will open to the left.

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