Question

If the tangents from the point $$\left( {\lambda ,\,3} \right)$$  to the ellipse $$\frac{{{x^2}}}{9} + \frac{{{y^2}}}{4} = 1$$   are at right angles then $$\lambda $$ is :

A. $$ \pm 1$$
B. $$ \pm 3$$
C. $$ \pm 2$$  
D. none of these
Answer :   $$ \pm 2$$
Solution :
The equation of the pair of tangents is $$S{S_1} = {T^2}$$
or $$\left( {\frac{{{x^2}}}{9} + \frac{{{y^2}}}{4} - 1} \right)\left( {\frac{{{\lambda ^2}}}{9} + \frac{9}{4} - 1} \right) = {\left( {\frac{{\lambda x}}{9} + \frac{{3y}}{4} - 1} \right)^2}$$
For right angle, $$a + b = 0 \Rightarrow \left\{ {\frac{1}{9}\left( {\frac{{{\lambda ^2}}}{9} + \frac{5}{4}} \right) - \frac{{{\lambda ^2}}}{{81}}} \right\} + \left\{ {\frac{1}{4}\left( {\frac{{{\lambda ^2}}}{9} + \frac{5}{4}} \right) - \frac{9}{{16}}} \right\} = 0$$

Releted MCQ Question on
Geometry >> Ellipse

Releted Question 1

Let $$E$$ be the ellipse $$\frac{{{x^2}}}{9} + \frac{{{y^2}}}{4} = 1$$   and $$C$$ be the circle $${x^2} + {y^2} = 9.$$   Let $$P$$ and $$Q$$ be the points $$\left( {1,\,2} \right)$$  and $$\left( {2,\,1} \right)$$  respectively. Then-

A. $$Q$$ lies inside $$C$$ but outside $$E$$
B. $$Q$$ lies outside both $$C$$ and $$E$$
C. $$P$$ lies inside both $$C$$ and $$E$$
D. $$P$$ lies inside $$C$$ but outside $$E$$
Releted Question 2

The radius of the circle passing through the foci of the ellipse $$\frac{{{x^2}}}{{16}} + \frac{{{y^2}}}{9} = 1,$$   and having its centre at $$\left( {0,\,3} \right)$$  is-

A. $$4$$
B. $$3$$
C. $$\sqrt {\frac{1}{2}} $$
D. $$\frac{7}{2}$$
Releted Question 3

The area of the quadrilateral formed by the tangents at the end points of latus rectum to the ellipse $$\frac{{{x^2}}}{9} + \frac{{{y^2}}}{5} = 1,$$    is-

A. $$\frac{{27}}{4}\,\,{\text{sq}}{\text{.}}\,{\text{units}}$$
B. $$9\,\,{\text{sq}}{\text{.}}\,{\text{units}}$$
C. $$\frac{{27}}{2}\,\,{\text{sq}}{\text{.}}\,{\text{units}}$$
D. $$27\,\,{\text{sq}}{\text{.}}\,{\text{units}}$$
Releted Question 4

If tangents are drawn to the ellipse $${x^2} + 2{y^2} = 2,$$   then the locus of the mid-point of the intercept made by the tangents between the coordinate axes is-

A. $$\frac{1}{{2{x^2}}} + \frac{1}{{4{y^2}}} = 1$$
B. $$\frac{1}{{4{x^2}}} + \frac{1}{{2{y^2}}} = 1$$
C. $$\frac{{{x^2}}}{2} + \frac{{{y^2}}}{4} = 1$$
D. $$\frac{{{x^2}}}{4} + \frac{{{y^2}}}{2} = 1$$

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Ellipse


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