Double integrals in polar coordinates

[noname1]

I was overlooking a problem that my teacher solved and i can't understand a step see took i was wondering if someone you tell me how she got from this step

Double integral rcos(o)(rsino)rto this

Double integral (r/2)^3(2sinocoso)

 

[Delzac]

From what you have written, i don't think it was possible for she to get from the 1st step to the second.

 

[noname1]

i don't see either, when i do i get to this step which i hope is correct(r²coso)(r²sino) => r^4cososino