I dz dx dy V V=5.257 y-4 2x+4c1-x 81 -Z CV2X+4V 03 6 y y3 - 4 2 1 x 01 - x 1 z óôõ d óôôõ d óôôõ := d V 81 28 3 ® × 6 V = 5.257 V1 - 2 1 x 03 2 x + 4 y 01 - x 1 z óôõ d óôõ d óôõ := d V1 81 28 3 ® × 6 V2 03 z - 2 1 - z x 03 2 x + 4 1 y óôõ d óôõ d óôõ := d V2 81 28 3 ® × 6