Maths-
General
Easy
Question
Tangents are drawn from the point (-1,2) on the parabola The length, these tangents will intercept on the line :
- 6
- 6
- 2
- none of these
Hint:
The correct answer is: 6
The length of tangent is asked to be find
if the line x=2 intersects these tangents at (x1,y1) and (x2,y2) then the length of the intercept is given by |y1−y2|
SS1=T2 is the equation of pair of tangents
(y2−4x)(8)=4(y−x+1)2
⇒y2−2y(1−x)−(x2+6x+1)=0
Put x=2
⇒y2+2y−17=0
Clearly, y1,y2 are the roots of the equation y2+2y−17=0
⇒y1+y2=−2
y1⋅y2=−17
Now, |y1−y2|=√(y1+y2)2−4y1⋅y2
=√22−4(−17)
=√72
=6√2
∴|y1−y2|=6√2
Hence finally the length is
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