If the common tangent to the parabolas,
y2 = 4x and x2 = 4y also touches the circle, x2 + y2 = c2,
then c is equal to :
Solution
$y = mx + {1 \over m}$ (tangent at y<sup>2</sup>
= 4x)
<br><br>y = mx – m<sup>2</sup>
(tangent at x<sup>2</sup>
= 4y)
<br><br>${1 \over m} = - {m^2}$ (for common tangent)
<br><br>m<sup>3</sup>
= – 1
<br><br>$\Rightarrow$ m = - 1
<br><br>$\therefore$ Equation of tangent
<br><br>y = –x –1
<br><br>x + y + 1 = 0
<br><br>This line touches circle whose center at (0, 0),
<br><br>$\therefore$ apply p( Distance from center of the circle of the line ) = r ( Radius of the circle )
<br><br>c = $\left| {{{0 + 0 + 1} \over {\sqrt 2 }}} \right| = {1 \over {\sqrt 2 }}$
About this question
Subject: Mathematics · Chapter: Conic Sections · Topic: Parabola
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