double integral of ydxdy
= integral of y^2/2+ c1 dx
= y^2x/2 +c1x + c2
where c1 and c2 are constants
plane area inside (x-1)^2 +(y-1)^2 =8 is area of a circle with radius sqr8
= pir^2 = 8pi
if you use integral calculus to find the circle's area you should get the same solution