2道数学题,还要用加减消元法,三元一次方程组：（一定要有过程和答案,还要用加减消元法,）① {x+y+z=43x+y-2z=02x+3y+z=7② {3x+2y+5z=2x-2y-z=64x+2y-7z=30

① {x+y+z=4 ①3x+y-2z=0 ②2x+3y+z=7 ③1×2+2,得5x+3y=8 ④3×2+2,得7x+7y=14 ⑤5化简,得x+y=2 ⑥由6,得x=2-y ⑦把7代入4,得y=1把y=1代入7,得x=1把y=1,x=1代入1,得z=2∴{x=1y=1z=2为所求 ② {3x+2y+5z=2① x-2y-z=...