1.∫∫D（x²-y²)dxdy =∫(0,π)dx∫(0,sinx)（x²-y²)dy =∫(0,π)dx[x²sinx - (sin³x)/3]=∫(0,π)[x²(-dcosx) + (sin²x)(dcosx)/3]=∫(0,π)[(1-cos²x)(dcosx)/3] - ...