How do you find the center and radius of the circle $x^2 + y^2 - 8y = 9$ ?

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Answer 1 · 2018-03-18T12:23:07

$"centre "(0,4), " radius "=5$

we complete the square

$x^2+y^2-8y=9$

$rarrx^2+(y^2-8y+4^2)-4^2=9$

$x^2+(y-4)^2-16=9$

$x^2+(y-4)^4=25$

cmp with the standard eqn

#"centre "(a,b)," radius "=r

$(x-a)^2+(y-b)^"=r^2$

we have

$"centre "(0,4), " radius "=5$

How do you find the center and radius of the circle x^2 + y^2 - 8y = 9x^2 + y^2 - 8y = 9?