logo

Ask Questions, Get Answers

 
X
 Search
Want to ask us a question? Click here
Browse Questions
Ad
Home  >>  CBSE XI  >>  Math  >>  Conic Sections
0 votes

Find the co-ordinates of the focus, axis of the parabola, equations of the directrix and length of latus rectum of the parabola $x^2=-9y$

$\begin{array}{1 1}(0,-2.25) \quad \text{y-axis} \quad y=2.25 \quad 9 \\ (0,2.25) \quad \text{y-axis} \quad y=-2.25 \quad 9 \\ (0,-2.25) \quad \text{x-axis} \quad y=2.25 \quad \large\frac{9}{4} \\ (0,-2.25) \quad \text{y-axis} \quad y=2.25 \quad \large\frac{9}{4} \end{array} $

Can you answer this question?
 
 

1 Answer

0 votes
Toolbox:
Given $x^2=-9y$
The co-efficient of $y$ is negative, The parabola opens downward. $x^2=9y \rightarrow -4a = -9\rightarrow a = 2.25$
1) Therefore co-ordinates of the focus = $(0,-a) = (0,-2.25)$
2) Since $x^2=-9y$, the axis of the parabola is the y-axis
3) The Equation of the directrix $ y = a \rightarrow y = 2.25$
4) The Length of the Latus Rectum $ = 4a =4 \times 2.25 = 9$
answered Apr 1, 2014 by balaji.thirumalai
 

Related questions

Ask Question
student study plans
x
JEE MAIN, CBSE, NEET Mobile and Tablet App
The ultimate mobile app to help you crack your examinations
Get the Android App
...