Question

If lx + my -1 = 0 touches the circle `x^2 + y^2 = a^2` then the point (l,m) lies on the circle

Answer 1

C(0,0),r=a
`d=|(0+0-1)/sqrt(l^2+m^2)|=a`
`1/(l^2+m^2)=a^2`
`l^2+m^2=1/a^2`
`l^2+m^2=a^(-2)`
`x^2+y^2=a^(-2)`
option C is correct.