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Mobile App Chapter 10: Q 10. (page 643)
Answer Problem using the figure.
If a = 4, then the equation of the directrix is______ .
Short Answer
If a = 4, then the equation of the directrix is
y = -2.
Step by step solution
Step 1. Given information.
We have given a = 4 and graph of parabola is,
Step 2. Concept used.
Directrix of the parabola:
The directrix is perpendicular to the axis of symmetry of a parabola and does not touch the parabola.
Formula for the directrix for upward parabola is: y = k - a.
Step 3. Explanation.
We have given graph is,
This parabola is upward parabola so directrix of the parabola is,
.
Where " k " is the y-coordinate of the vertex.
From figure we have vertex = (3, 2).
So equation for the directrix is,
y = 2 - 4 = -2.
Step 4. Conclusion.
If a = 4, then the equation of the directrix is y = -2.
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