3X+2Y-Z=1 ①
X-2Y+2Z=5 ②
5X-2Y+5Z=11 ③
①+②得4x+z=6 ⑤
③-②得4x+3z=6 ⑥
⑤-⑥得z=0
将z=0代入⑤的x=3/2
将x=3/2代入9/2+2y=1
y=-7/4
所以x=3/2 y=-7/4 z=0