If the length of the latus rectum of a parabola, whose focus is $(a, a)$ and the tangent at its vertex is $x+y=a$, is 16, then $|a|$ is equal to :
Solution
<p>Equation of tangent at vertex : $L \equiv x + y - a = 0$</p>
<p>Focus : $F \equiv (a,a)$</p>
<p>Perpendicular distance of L from F</p>
<p>$$ = \left| {{{a + a - a} \over {\sqrt 2 }}} \right| = \left| {{a \over {\sqrt 2 }}} \right|$$</p>
<p>Length of latus rectum $= 4\left| {{a \over {\sqrt 2 }}} \right|$</p>
<p>Given $4\,.\,\left| {{a \over {\sqrt 2 }}} \right| = 16$</p>
<p>$\Rightarrow |a| = 4\sqrt 2$</p>
About this question
Subject: Mathematics · Chapter: Conic Sections · Topic: Parabola
This question is part of PrepWiser's free JEE Main question bank. 146 more solved questions on Conic Sections are available — start with the harder ones if your accuracy is >70%.