{4x-5y+2z=0 3x+2y+7z=28 x-y+2z=5
问题描述：
{4x-5y+2z=0 3x+2y+7z=28 x-y+2z=5
答
4x-5y+2z=0 ①
3x+2y+7z=28 ②
x-y+2z=5 ③
③X4 -① 得 Y+6Z=20 ④
②- ③X3 得 5Y+Z =13 ⑤
⑤X6 -④ 得 29Z =87
所以 Z=3
带入④得 Y=2
Z=3 Y=2 带入 ① 解得 X=1
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