1、标① 和②2、变形和标③3、代入并求解4、再代5、写解解：原程组可化为：①②由①得：x = 2 – 3y③把③代入②得：-2（2 – 3y）+ 6y = 1-4 + 6y + 6y = 16y + 6y = 1 + 412y = 5y = 5/12把y = 5/12 代入③，得x = 2 – 3y= 2 - 3×5/12x = 3/4∴x = 3/4y = 5/12解：原程组可化为：3x – 2y = 6x – y = 2①②由②得：把③代入①得：x = 2 + y③3（2 + y）- 2y = 66 + 3y – 2y = 6y = 0把y = 0 代入③，得：x = 2 + y= 2 + 0x = 2∴x = 2y = 0解程组：3.练 习 题1、若程5x 2m+n+4y 3m-2n = 9是关x、y的二元一次程，求m 、n 的值.解：根据已知条件得：2m + n = 13m – 2n = 1①②由①得：把③代入②得：n = 1 –2m③3m – 2（1 – 2m）= 13m – 2 + 4m = 17m = 3m = 3/7把m = 3/7 代入③，得：n = 1 –2m4.思 考 题2、已知 是关 x、y 的程组 的解，求 a 、 b 的值.x =-1，y = 2，-2 + 2a = 3b-a – 2b = 1①②5.思 考 题由②得：a = -2b - 1③把③代入①得：-2 + 2（-2b – 1）= 3b-2 – 4b – 2 = 3b-4b – 3b = + 2 + 2-7b = 4b = -4/7把b = -4/7 代入③，得：a = 1/7∴a = 1/7b = -4/7a = -2b - 1= -2×（-4/7）-16.思 考 题解：①②由①得：y = 2x - 3③把③代入②得：3x + 2（2x – 3）= 83x + 4x – 6 = 83x + 4x = 8 + 67x = 14x = 2把x = 2 代入③，得：y = 2x - 3= 2×2 - 3=1④⑤解得：a = 1b = -17.思 考 题4、如果∣y + 3x - 2∣+∣5x + 2y -2∣= 0，求 x 、y 的值.解：根据已知条件，得：①②由①得：y = 2 – 3x把③代入②得：③5x + 2（2 – 3x）- 2 = 05x + 4 – 6x – 2 = 05x – 6x = 2 - 4-x = -2x = 2把x = 2 代入③，得：y = 2 |
