Q.Find the coordinates of the focus, axis of the parabola, the equation of the directrix and the length of the latus rectum of the parabola .
The parabola opens upward with vertex at the origin; comparing with gives , so the focus is , directrix , axis the -axis, and latus rectum .
Why this form tells us everything
A parabola is the locus of points equidistant from a fixed point (the focus) and a fixed line (the directrix). When the equation is written as , the parabola has its vertex at the origin and opens along the -axis. The parameter encodes the "focal distance"—how far the focus sits from the vertex—and from it we can read off every geometric feature.
The standard form describes a parabola that:
- has vertex at ,
- opens upward if (downward if ),
- has focus at ,
- has directrix ,
- has the -axis as its axis of symmetry,
- has latus rectum (the chord through the focus perpendicular to the axis) of length .
Our task is to identify and then extract these features.
Step-by-step extraction
1. Identify the parameter
We have . Comparing with the standard form , we see
Since , the parabola opens upward.
2. Find the focus
The focus of lies at . Substituting ,
3. Write the equation of the directrix
The directrix is the horizontal line . With ,
4. State the axis of the parabola
The axis of symmetry is the line passing through the vertex and focus, perpendicular to the directrix. Here it is the -axis, or
5. Calculate the length of the latus rectum
The latus rectum is the chord through the focus perpendicular to the axis. Its length is always . Thus
For any parabola , the latus rectum length is simply the coefficient of —here —so you can read it directly without computing separately.
Summary table
| Feature | Value |
|---|---|
| Focus | |
| Directrix | |
| Axis | (the -axis) |
| Latus rectum length |
The focus is , the axis is the line , the directrix is , and the length of the latus rectum is .
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