2020-2021学年2 求解二元一次方程组图片ppt课件

这是一份2020-2021学年2 求解二元一次方程组图片ppt课件，共31页。
解：由①得 x=y+2 ③
x-y=2 ①x+2y=5 ②
∴原方程组的解是
解得 y=1 把 y=1代入③得 x=3
把③代入②得 y+2+2y=5
2000x+1999y=3999 ①999x-1999y=-1000 ②
2000x +1999y = 3999 ① 999x -1999y = -1000 ②
解：由①+②得 2999x=2999 解得 x=1 把 x=1代入①得 2000+1999y=3999 解得 y=1 ∴原方程组的解是
2000x+1999y=3999 ①999x-1999y=-1000 ②
2x-5y=7 ①2x+3y=-1 ②
参考以上思路，怎样解下面类似的二元一次方程组呢？
2x -5y = 7 ① 2x +3y = -1 ②
解：由①-②得 -8y=8 解得 y=-1 把 y=-1代入①得 2x+5=7 解得 x=1 ∴原方程组的解是
2x-5y=7 ①2x+3y=-1 ②
未知数系数互为相反数时，加法消元
未知数系数相等时，减法消元
未知数的系数相等或互为相反数
3x-4y=2 ①2x+5y=9 ②
怎样解下面的二元一次方程组呢？
解：由①×2得 6x-8y=4 ③ 由②×3得 6x+15y=27 ④
③-④得 -23y=-23 解得 y=1
把 y=1代入①得 3x-4=2 解得 x=2
解：由①×5得 15x-20y=10 ③ 由②×4得 8x+20y=36 ④
③+④得 23x=46 解得 x=2
把 x=2代入①得 6-4y=2 解得 y=1
∴原方程组的解是
4x-3y=14 5x+3y=31
用加减消元法解下列方程组：
4x+7y=18 4x-5y=-6
2x-5y=-21 4x+3y=23
2x-5y=1 7x-3y=18
将二元方程转化为一元方程！
33x+17y=83 ①17x+33y=67 ②
求解下面的二元一次方程组.
Never give up, Never lse hpe. Always have faith, It allws yu t cpe. Trying times will pass, As they always d.
Presentatins are tls that can be used as lectures.
Never give up, Never lse hpe. Always have faith, It allws yu t cpe. Trying times will pass, As they always d. Just have patience, Yur dreams will cme true. Never give up, Never lse hpe. Always have faith, It allws yu t cpe. Trying times will pass, As they always d. Just have patience, Yur dreams will cme true. Always have faith, It allws yu t cpe. Trying times will pass, As they always d. Just have patience, Yur dreams will cme true.
Presentatins are tls that can be used as lectures.Presentatins are tls that can be used as lectures.
Never give up, Never lse hpe. Always have faith, It allws yu t cpe. Trying times will pass, As they always d. Just have patience, Yur dreams will cme true. Never give up, Never lse hpe. Always have faith, It allws yu t cpe. Trying times will pass, As they always d. Just have patience, Yur dreams will cme true. Always have faith, It allws yu t cpe. Trying times will pass, As they always d. Just have patience, Yur dreams will cme true.
Presentatins are tls that can be used lectures.Presentatins are tls that can be used as lectures.
解：由①+②得 9x=45 解得 x=5 把 x=5代入①得 20-3y=14 解得 y=2 ∴原方程组的解是
4x-3y=14 ① 5x+3y=31 ②
2x-5y=-21 ① 4x+3y=23 ②
解：由①×2得 4x-10y=-42 ③ ③-②得 13y=65 解得 y=5
把 y=5代入②得 4x+15=23 解得 x=2
解：由①-②得 12y=24 解得 y=2 把 y=2代入①得 4x+14=18 解得 x=1 ∴原方程组的解是
4x+7y=18 ① 4x-5y=-6 ②
2x-5y=1 ① 7x-3y=18 ②
解：由①×7得 14x-35y=7 ③ 由②×2得 14x-6y=36 ④ ③-④得 -29y=-29 解得 y=1
把 y=1代入①得 2x-5=1 解得 x=3