JEE Advance - Mathematics (2022 - Paper 1 Online - No. 8)
Explanation
Here ABC is a right angle triangle. BC is the Hypotenuse of the triangle.
We know, diameter of circumcircle of a right angle triangle is equal to the Hypotenuse of the triangle also midpoint of Hypotenuse is the center of circle.
$$\therefore$$ $$BC$$ = Diameter of the circle
Here $$B = (0,1)$$ and $$C(3,0)$$
$$\therefore$$ $$BC = \sqrt {{3^2} + {1^2}} $$
$$ = \sqrt {9 + 1} $$
$$ = \sqrt {10} $$
$$\therefore$$ Radius of circumcircle $$(R) = {{\sqrt {10} } \over 2}$$
$$\therefore$$ Center of circle $$(M) = \left( {{{3 + 0} \over 2},\,{{0 + 1} \over 2}} \right) = \left( {{3 \over 2},\,{1 \over 2}} \right)$$
Center of circle which touches line AB and AC $$ = (r,r)$$
Now distance between center of two circles,
$$ME = R - r = {{\sqrt {10} } \over 2} - r$$
$$ \Rightarrow {\left( {r - {3 \over 2}} \right)^2} + {\left( {r - {1 \over 2}} \right)^2} = {\left( {{{\sqrt {10} } \over 2} - r} \right)^2}$$
$$ \Rightarrow {r^2} - 3r + {9 \over 4} + {r^2} - r + {1 \over 4} = {{10} \over 4} + {r^2} - \sqrt {10} r$$
$$ \Rightarrow {r^2} - 4r + \sqrt {10} r = 0$$
$$ \Rightarrow r(r - 4 + \sqrt {10} ) = 0$$
$$ \Rightarrow r = 0$$ or $$r = r - \sqrt {10} $$
$$\therefore$$ $$r = 4 - \sqrt {10} $$ [as $$r \ne 0$$]
$$ = 0.837$$
$$ \simeq 0.84$$
Comments (0)
