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Question

Length of chord of contact of (2,5) with respect to y2=8x is

A
3412 units
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B
2173 units
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C
735 units
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D
537 units
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Solution

The correct option is A 3412 units
Chord of contact of (2,5) with respect to y2=8x is
y5=4(x+2)
5y4x=8 (1)
Solving equation (1) with y2=8x
y2=(5y8)2
y210y+16=0
(y8)(y2)=0
y1=8,y2=2
Using (1), we get
x1=8,x2=12
Then the end points of chord are (8,8) and (12,2)
So, length of chord of contact
=(812)2+(82)2
=3412 units

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