1.

Find the centre and radius of the circles`x^2+y^2-4x-8y-45=0`

Answer» `x^(2)+y^(2)-4x-8y-45=0`
Comparing with `x^(2)+y^(2)+gx+2fy+c=0`
`2g=-4,2f=-8,c=-45`
`rArr" "g=-2,f=-4,c=-45`
`:.` Centre of circle `-=(-g,-f)-=(2,4)`
and radius `r=sqrt(g^(2)+f^(2)-c)`
`=sqrt((2)^(2)+(4)^(2)-(-45))`
`sqrt(4+16+45)=sqrt(65)` units


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