∑：z=1 - x - ydz = - dx - dy ∫∫dS = ∫√(1+(-1)^2+(-1)^2)dxdy= √3∫(0,1)dx∫(0,1-x)dy= √3∫(0,1)(1-x)dx= √3(x - x^2/2)[0,1]= √3/2
