13X+5Y+9Z=12.7------⑴2X+4Y+3Z=4.7--------⑵求X+Y+Z的值。式⑵×3得：6X+12Y+9Z=14.1------⑶⑴-⑶得：7X-7Y=-1.4 X-Y=-0.2 代入⑴得：13X+5（X+0.2）+9Z=12.7 18X+9Z=11.72X+Z=1.3 又：Y=X+0.2所以X+Y+Z-0.2=1.3X+Y+Z=1.5
