拓展:1,已知:{3x+y+2z=285x-3y+z=7求:x+y+z的值
3x + y + 2z =28;①
①乘以3,9x + 3y + 6z = 84; ②
5x - 3y + z =7; ③
③ + ②,14x + 7z = 91,除以7,2x + z = 13; ④
③ 乘以2,10x - 6y + 2z = 14;⑤
⑤ - ①,7x - 7y = -14,除以7,x - y = -2;⑥
④ - ⑥,x + y + z = 15 。
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3x + y + 2z =28;①
①乘以3,9x + 3y + 6z = 84; ②
5x - 3y + z =7; ③
③ + ②,14x + 7z = 91,除以7,2x + z = 13; ④
③ 乘以2,10x - 6y + 2z = 14;⑤
⑤ - ①,7x - 7y = -14,除以7,x - y = -2;⑥
④ - ⑥,x + y + z = 15 。