Question

The vertex of the parabola $${y^2} = 8x$$  is at the centre of a circle and the parabola cuts the circle at the ends of its latus rectum. Then the equation of the circle is :

A. $${x^2} + {y^2} = 4$$
B. $${x^2} + {y^2} = 20$$  
C. $${x^2} + {y^2} = 80$$
D. none of these
Answer :   $${x^2} + {y^2} = 20$$
Solution :
Vertex $$ = \left( {0,\,0} \right)$$   The ends of latus rectum are $$\left( {2,\,4} \right)\left( {2,\, - 4} \right)$$
$$\therefore $$  centre $$ = \left( {0,\,0} \right)$$   radius $$ = \sqrt {{2^2} + {4^2}} = \sqrt {20} $$

Releted MCQ Question on
Geometry >> Parabola

Releted Question 1

Consider a circle with its centre lying on the focus of the parabola $${y^2} = 2px$$   such that it touches the directrix of the parabola. Then a point of intersection of the circle and parabola is-

A. $$\left( {\frac{p}{2},\,p} \right){\text{ or }}\left( {\frac{p}{2},\, - p} \right)$$
B. $$\left( {\frac{p}{2},\, - \frac{p}{2}} \right)$$
C. $$\left( { - \frac{p}{2},\,p} \right)$$
D. $$\left( { - \frac{p}{2},\, - \frac{p}{2}} \right)$$
Releted Question 2

The curve described parametrically by $$x = {t^2} + t + 1,\,\,y = {t^2} - t + 1$$      represents-

A. a pair of straight lines
B. an ellipse
C. a parabola
D. a hyperbola
Releted Question 3

If $$x+y=k$$   is normal to $${y^2} = 12x,$$   then $$k$$ is-

A. $$3$$
B. $$9$$
C. $$ - 9$$
D. $$ - 3$$
Releted Question 4

If the line $$x-1=0$$   is the directrix of the parabola $${y^2} - kx + 8 = 0,$$    then one of the values of $$k$$ is-

A. $$\frac{1}{8}$$
B. $$8$$
C. $$4$$
D. $$\frac{1}{4}$$

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Parabola


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