Circle: x 2+y 2 = (2a) 2

The part in the first quadrant

Die first, then dx.

The geometric meaning of double integral is the area of the figure.

Now we know that the graph is a circle: x 2+y 2 = (2a) 2.

The part in the first quadrant

So it is π * 4a 2/4 = π a 2.

Give more points.