Precalculus : Pre-Calculus

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Understand Features Of Hyperbolas And Ellipses

Find the equation of an ellipse centered at the origin if the major axis is parallel to the x-axis and has a length of  units and the minor axis has a length of  units.

Possible Answers:

Correct answer:

Explanation:

The formula for an ellipse centered at the point  with a horizontal major axis (ie: parallel to the x-axis) has the formula

 

where  and  are the lengths of the major and minor axes respectively.

Since the origin is at  and  and  in this problem, the equation is

or

Example Question #1 : Understand Features Of Hyperbolas And Ellipses

The equation of an ellipse, , is . Which of the following is the correct center and foci of this ellipse?

Possible Answers:

Center=, Foci= and 

Center=, Foci= and 

Center=, Foci= and 

Center=, Foci= and 

Center=, Foci= and 

Correct answer:

Center=, Foci= and 

Explanation:

Because our equation is already in the format

 ,

we do not have to manipulate the equation. The center of any ellipse in this form will always be . So in this case, our center will be . To find the foci of the ellipse, we must use the equation , where  is the greater of the two denominators in our equation ( and ),  is the lesser and  is the distance from the center to the foci.

We know that  and .

By using , we see that , so .

We now know that the two foci are going to be  units in either direction of the center along the greater axis.

Because the greater denominator is under our term containing , our ellipse will have its greater axis going vertically, rather than horizontally. Therefore, our foci will be  units above and below our center, at  and .

Example Question #4 : Hyperbolas And Ellipses

Find the center of the ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Recall that the standard form of the equation of an ellipse is

, where  is the center for the ellipse.

For the equation given in the question,  and 

The center of the ellipse is at 

 

Example Question #4 : Understand Features Of Hyperbolas And Ellipses

Find the center of the ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Recall that the standard form of the equation of an ellipse is

, where  is the center for the ellipse.

For the equation given in the question,  and 

The center of the ellipse is at .

 

Example Question #11 : Hyperbolas And Ellipses

Find the center of the ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Recall that the standard form of the equation of an ellipse is

, where  is the center for the ellipse.

For the equation given in the question,  and 

The center of the ellipse is at .

 

Example Question #11 : Hyperbolas And Ellipses

Find the center of the ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Start by putting the equation back into the standard equation of the ellipse:

, where  is the center for the ellipse.

 

Group the  terms and  terms together.

Factor out a  from the  terms, and a  from the  terms.

Now, complete the square. Remember to add the same amounts on both sides of the equation.

Now, divide both sides by .

Finally, factor the equations to get the standard form of the equation for an ellipse.

Since  and , the center for this ellipse is .

Example Question #12 : Hyperbolas And Ellipses

Find the center of the ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Start by putting the equation back into the standard equation of the ellipse:

, where  is the center for the ellipse.

 

Group the  terms and  terms together.

Factor out a  from the  terms and a  from the  terms.

Now, complete the squares. Make sure you add the same amount on both sides!

Subtract  from both sides.

Now, divide both sides by .

Finally, factor the terms to get the standard form of the equation of an ellipse.

Since  and , the center of the ellipse is .

Example Question #11 : Understand Features Of Hyperbolas And Ellipses

Find the center of the ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Start by putting the equation back into the standard equation of the ellipse:

, where  is the center for the ellipse.

 

Group the  terms and  terms together.

Factor out a  from the  terms and a  from the  terms.

Now, complete the squares. Remember to add the same amount on both sides!

Subtract  from both sides.

Divide both sides by .

Finally, factor the terms to get the standard form of the equation of an ellipse.

Since  and  is the center of this ellipse.

Example Question #15 : Understand Features Of Hyperbolas And Ellipses

Find the foci of an ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Recall that the standard form of the equation of an ellipse is

, where  is the center for the ellipse.

When , the major axis will lie on the -axis and be horizontal. When , the major axis will lie on the -axis and be vertical.

Recall also that the distance from the center to a focus, , is given by the equation  when , and the equation is  when .

When the major axis follows the -axis, the points for the foci are  and .

When the major axis follows the -axis, the points for the foci are  and .

 

For the given equation, the center is at . Since , the major-axis is vertical.

Plug in the values to solve for .

Now, add  to the y-coordinate of the center to get one focus. Subtract  from the y-coordinate of the center to get the other focus point.

The foci for the ellipse is then  and .

Example Question #106 : Conic Sections

Find the foci of the ellipse with the following equation:

Possible Answers:

Correct answer:

Explanation:

Recall that the standard form of the equation of an ellipse is

, where  is the center for the ellipse.

When , the major axis will lie on the -axis and be horizontal. When , the major axis will lie on the -axis and be vertical.

Recall also that the distance from the center to a focus, , is given by the equation  when , and the equation is  when .

When the major axis follows the -axis, the points for the foci are  and .

When the major axis follows the -axis, the points for the foci are  and .

 

Start by putting the equation into the standard form of the equation of an ellipse.

Group the  and  terms together.

Now, factor out a  from the  terms and a  from the  terms.

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

Subtract  from both sides of the equation.

Divide both sides by .

Factor both terms to get the standard form of the equation of an ellipse.

Now, the center for this ellipse is  and its major axis is horizontal.

Next, solve for .

The foci for this ellipse are then at  and .

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