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The line $4x+2y=c$ is a tangent to the parabola $y^{2}=16x$ then $c$ is

\[\begin{array}{1 1}(1)-1&(2)-2\\(3)4&(4)-4\end{array}\]

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$y^2=16x$
$y^2=4(4)x => a=4$
$4x+2y=c=> 2y=-4x+c$
$y= -\large\frac{4}{2}x + \frac{c}{2}$
$y= -2x+\large\frac{c}{2}$
Comparing with the equitation $y= mx+c$
$m= -2, c= \large\frac{c}{2}$
$ \large\frac{c}{2} =\frac{4}{-2} $
$c= -4$
Hence 4 is the correct answer.
answered May 15, 2014 by meena.p
 
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