Conic Sections Question 55
Question: The line $ lx+my+n=0 $ will touch the parabola $ y^{2}=4ax $ , if
[RPET 1988; MNR 1977; MP PET 2003]
Options:
A) $ mn=al^{2} $
B) $ lm=an^{2} $
C) $ ln=am^{2} $
D) $ mn=al $
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Answer:
Correct Answer: C
Solution:
$ y=-\frac{l}{m}x-\frac{n}{m} $
Condition for above line to be tangent to $ y^{2}=4ax $ is $ -\frac{n}{m}=\frac{am}{-l} $ or $ nl=am^{2} $ .
BETA
