Conic Sections

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Pre-Calculus › Conic Sections

Questions 1 - 10
1

Write the equation for in standard form

Explanation

To determine the standard-form equation, we'll have to complete the square for both x and y. It will be really helpful to re-group our terms to do that:

Adding 9 will complete the square for x, since

Adding 16 will complete the square for y, since

Now we just need to simplify. Re-write the left side as two binomials squared, and add the numbers on the right side:

2

Determine the equation for a circle in standard form, centered at (3,-4), with radius 2.

Explanation

Recall that the standard from for the equation of a circle is

where (h, k) is the center, and r is the radius. We are given the center (3, -4) and radius 2. Therefore, h = 3, k = -4, and r = 2. Plugging these vaules into the equation gives us

3

Describe the orientation of a parabola with the following equation:

Facing down

Facing up

Facing to the left

Facing to the right

None of the other options

Explanation

The coefficient of the squared term tells us whether the parabola faces up or down. Parabolas in general, as in the parent function, are in the shape of a U. In the equation given, the coefficient of the squared term is . Generally, if the coefficient of the squared term is positive, the parabola faces up. If the coefficient is negative, the parabola faces down. Since is negative, our parabola must face down.

4

How can this graph be changed to be the graph of

?

Wrong hyperbola 1

The -intercepts should be at the points and .

The graph should have -intercepts and not -intercepts.

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

The graph should be an ellipse and not a hyperbola.

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.

5

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

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

.

6

Geo_8_sec_6_graphik_3

If each mark on the graph represents units, what is the equation of the circle?

Explanation

Since the circle is centered at we use the most basic form for the equation for a circle:

.

Given the circle has a radius of marks, which represent units each, the circle has a radius of units.

We then plug in for :

and simplify: .

7

Write the equation for in standard form

Explanation

To determine the standard-form equation, we'll have to complete the square for both x and y. It will be really helpful to re-group our terms to do that:

Adding 9 will complete the square for x, since

Adding 16 will complete the square for y, since

Now we just need to simplify. Re-write the left side as two binomials squared, and add the numbers on the right side:

8

Determine the equation for a circle in standard form, centered at (3,-4), with radius 2.

Explanation

Recall that the standard from for the equation of a circle is

where (h, k) is the center, and r is the radius. We are given the center (3, -4) and radius 2. Therefore, h = 3, k = -4, and r = 2. Plugging these vaules into the equation gives us

9

How can this graph be changed to be the graph of

?

Wrong hyperbola 1

The -intercepts should be at the points and .

The graph should have -intercepts and not -intercepts.

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

The graph should be an ellipse and not a hyperbola.

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.

10

How can this graph be changed to be the graph of

?

Wrong hyperbola 1

The -intercepts should be at the points and .

The graph should have -intercepts and not -intercepts.

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

The graph should be an ellipse and not a hyperbola.

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.

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