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

7.  Find the centre and radius of the circles.

      x^2 + y^2 -4x - 8y - 45 = 0

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As we know, 

The equation of the circle with centre ( h, k) and radius r is given by ;

(x-h)^2+(y-k)^2=r^2

Given here 

x^2 + y^2 -4x - 8y - 45 = 0

Can also be written in the form 

(x-2)^2 + (y-4)^2 =(\sqrt{65})^2

So, from comparing, we can see that 

r=\sqrt{65}

Hence the Radius of the circle is \sqrt{65}.

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