Find the centre and radius of each of the following circles:

x2 + y2 - 4x + 6y = 5

Given that we need to find the centre and radius of the given circle x2 + y2 - 4x + 6y = 5.



We know that the standard equation of a circle with centre (a, b) and having radius ‘r’ is given by:


(x - a)2 + (y - b)2 = r2 - - - - - (1)


Let us convert given circle’s equation into the standard form.


x2 + y2 - 4x + 6y = 5


(x2 - 4x + 4) + (y2 + 6y + 9) = 5 + 4 + 9


(x - 2)2 + (y + 3)2 = 18


(x - 2)2 + (y - ( - 3))2 = (3)2 - - - (2)


Comparing (2) with (1), we get


Centre = (2, - 3) and radius = 3


The centre and radius of the circle is (2, - 3) and 3.


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