Q.

If the tangents to the hyperbola x29y2=9 ate drawn from point (3, 2), then

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a

equation of one of the tangents is 5x12y+9=0

b

equation of one of the tangents is x =3

c

the area of triangle that these tangents form with their chord of contact is 8 sq. units

d

the area of triangle that these tangents form with their chord of contact is 12 sq. units

answer is A, B, D.

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Detailed Solution

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Given hyperbola is x29y2=9

or x29y21=1

Equation of tangent is 

y=mx±a2m2b2

This tangent passes through (3,2). 

so,2=3m±9m214+9m212m=9m2=1m1=5/12 and m2=

So, equations of tangents are

y2=(5/12)(x3)5x12y+9=0       (1)and x=3              (2)

Now, equation of chord of contact w.r.t. point P(3,2) is

T=03x18y=9x6y=3       (3)

Solving (1) and (3), we get x=5,y=43.

Solving (2) and (3), we get x=3,y=0

Thus, vertices of triangle are  (3,2),(3,0),(5,4/3)

area of triangle=123213015431=12×3432(3+5)+1(4)=12|4164|=8 sq. units  

 

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