Sunday, December 11, 2011

Find the equation of the circle whose center (0,13) and the area = 25pi.

We'll write the equation of the circle in standard
form:


(x-h)^2 + (y-k)^2 = r^2, where h and k are the
coordinates of the center of the circle.


We'll identify h
and k:


h = 0 and k = 13


Now,
we'll determine the radius of the circle, using the formula for area of the
circle:


A = pi*r^2


25*pi =
pi*r^2


We'll divide by pi:


r^2
= 25


r = 5


We'll accept only
the positive value, since it is about a radius of a circle and it cannot be
negative.


Now,we'll substitute the coordinates of the
center of the circle and the value of radius in the equation of the
circle:


x^2 + (y - 13)^2 =
25


If we'll expand the square, we'll obtain
the general form of the equation:


x^2 + y^2 - 26y + 169 -
25 = 0


x^2 + y^2 - 26y  + 144 =
0

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