Hello, can anyone help me with this?

The first step is

dGt=(4*pi*dxdy/lambda)

So, dP1=dGt(y power of 2)

then P1 = 4*pi (integration y power of 2) dxdy

= 4*pi * x * (y3/3)

(this is the answer)

but if my 2nd step is dP1=(dGt)*(dGt)(y power of 4)

then it will become

P1= (4*pi/lambda)power of 2 (integration integration y power of 4 dxdy dxdy)

How am i suppose to settle this, should i use the U. dv integration of I have to part by part..

Plz help me

TQ in advance