If slope of the focal chord of parabola y2=8x is the greater root of the equation x2−6x+8=0, then length of the focal chord will be
A
10 units
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B
17 units
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C
174 units
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D
172 units
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Solution
The correct option is D172 units x2−6x+8=0
Roots are 2 and 4.
Slope =tanα=4 ⇒cosec2α=1716 a=2
Now length of focal chord is 4acosec2α=4×2×1716 =172 units