Friday, December 3, 2010

What is the area of the circle whose equation is x^2 + y^2 - 2x + 4y = 32

Given the equation of the circle
is:


x^2 + y^2 -2x + 4y = 32


We
need to find the area of the circle.


To find the area, we
need to determine the radius of the circle (r).


We can
determine r by rewriting the circle equation into the standard
form.


 (x-a)^2 + (y-b)^2 = r^2 where r is the
radius.


Let us rewrite by completing the
square.


==> x^2 + y^2 - 2x + 4y =
32


==> x^2 - 2x + y^2 + 4y =
32


==> x^2 - 2x + 1 -1 + y^2 + 4y + 4 - 4 =
32


==> (x-1)^2 -1 + ( y+2)^2 - 4 =
32


==> (x-1)^2 + (y+2)^2 = 32 +
5


==> (x-1)^2 + (y+2)^2 =
37


Then, we conclude that r^2 =
37.


==> r=
sqrt(37).


Now we will determine the
area.


==> The area (a )= r^2 * pi =
37*pi = 116.24 square units (approx.)

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