# High School Math : Conic Sections

## Example Questions

### Example Question #1 : Circles

What is the center and radius of the circle indicated by the equation?      Explanation:

A circle is defined by an equation in the format .

The center is indicated by the point and the radius .

In the equation , the center is and the radius is .

### Example Question #5 : Conic Sections

What is the shape of the graph indicated by the equation? Circle

Parabola

Ellipse

Hyperbola

Ellipse

Explanation:

An ellipse has an equation that can be written in the format . The center is indicated by , or in this case .

### Example Question #1 : Conic Sections

A conic section is represented by the following equation: What type of conic section does this equation represent?

Parabola

Circle

Hyperbola

Ellipse

Hyperbola

Explanation:

The simplest way to know what kind of conic section an equation represents is by checking the coefficients in front of each variable. The equation must be in general form while you do this check. Luckily, this equation is already in general form, so it's easy to see. The general equation for a conic section is the following: Assuming the term is 0 (which it usually is):

• If A equals C, the equation is a circle.
• If A and C have the same sign (but are not equal to each other), the equation is an ellipse.
• If either A or C equals 0, the equation is a parabola.
• If A and C are different signs (i.e. one is negative and one is positive), the equation is a hyperbola.

### Example Question #2 : Conic Sections

A conic section is represented by the following equation: Which of the following best describes this equation?

horizontal hyperbola with center of and asymptotes with slopes of and vertical hyperbola with center and asymptotes with slopes of and vertical parabola with vertex and a vertical stretch factor of vertical ellipse with center and a major axis length of horizontal hyperbola with center and asymptotes with slopes of and horizontal hyperbola with center of and asymptotes with slopes of and Explanation:

First, we need to make sure the conic section equation is in a form we recognize. Luckily, this equation is already in standard form: The first step is to determine the type of conic section this equation represents. Because there are two squared variables ( and ), this equation cannot be a parabola.  Because the coefficients in front of the squared variables are different signs (i.e. one is negative and the other is positive), this equation must be a hyperbola, not an ellipse.

In a hyperbola, the squared term with a positive coefficient represents the direction in which the hyperbola opens. In other words, if the term is positive, the hyperbola opens horizontally. If the term is positive, the hyperbola opens vertically. Therefore, this is a horizontal hyperbola.

The center is always found at , which in this case is .

That leaves only the asymptotes. For a hyperbola, the slopes of the asymptotes can be found by dividing by (remember to always put the vertical value, , above the horizontal value, ). Remember that these slopes always come in pairs, with one being positive and the other being negative.

In this case, is 3 and is 2, so we get slopes of and .

### Example Question #3 : Conic Sections

Find the vertex for a parabola with equation       Explanation:

For any parabola of the form ,  the -coordinate of its vertex is So here, we have  We plug this back into the original equation to find :  ### Example Question #4 : Conic Sections

What is the minimal value of over all real numbers?   No minimum value.  Explanation:

Since this is an upwards-opening parabola, its minimum value will occur at the vertex.  The -coordinate for the vertex of any parabola of the form is at So here,   We plug this value back into the equation of the parabola, to find the value of the function at this   Thus the minimal value of the expression is ### All High School Math Resources 