- Home
- Standard 11
- Mathematics
10-1.Circle and System of Circles
easy
The equation of the normal at the point $(4,-1)$ of the circle $x^2+y^2-40 x+10 y=153$ is
A
$x + 4y = 0$
B
$4x + y = 3$
C
$x - 4y = 0$
D
$4x - y = 0$
Solution
Equation of circle-
$x^2+y^2-40 x+10 y=153$
$\Rightarrow(x-20)^2+(y+5)^2-25-400=153$
$\Rightarrow(x-20)^2+(y+5)^2=578$
Centre of circle $\equiv(20,-5)$
As we know that normal to the circle passes through its centre.
$\therefore$ Equation of normal to the circle $x ^2+ y ^2-40 x +10 y =153$ at $(4,-1)$ will be
$( y -(-1))=\frac{-5-(-1)}{20-4}( x -4)$
$\Rightarrow y +1=-\frac{1}{4}( x -4)$
$\Rightarrow 4( y +1)=4- x$
$\Rightarrow x +4 y =0$
Hence the equation of normal to the circle $x ^2+ y ^2-40 x +10 y =153$ at $(4,-1)$ is $x +4 y =0$
Standard 11
Mathematics