初中數(shù)學(xué)八年級上 求解二元一次方程組——加減消元法 課件

1、求解二元一次方程組（2） 加減消元法南山區(qū)文理實驗（集團）科創(chuàng)學(xué)校 陳秀瓊北師大版 八上數(shù)學(xué)代入消元法代入消元消元解：由得 x=y+2 x-y=2 x+2y=5 x=3 y=1變形求解寫解代入 原方程組的解是 解得 y=1 把 y=1代入得 x=3 把代入得 y+2+2y=5代入法慫了代入消元2000 x+1999y=3999 999x-1999y=-1000 由得 代入法慫了 2000 x +1999y = 3999 999x -1999y = -1000 2999x2999=0 x1=+ 2000 x+1999y=3999 999x-1999y=-1000 + 解：由+得 2999x=29

2、99 解得 x=1 把 x=1代入得 2000+1999y=3999 解得 y=1 原方程組的解是 代入法慫了2000 x+1999y=3999 999x-1999y=-1000 x=1 y=1加減消元法1999y=1999加減消元法2x-5y=7 2x+3y=-1 參考以上思路，怎樣解下面類似的二元一次方程組呢？ 2x -5y = 7 2x +3y = -1 -8y8 =0-1=- + y解：由-得 -8y=8 解得 y=-1 把 y=-1代入得 2x+5=7 解得 x=1 原方程組的解是 加減消元法2x-5y=7 2x+3y=-1 x=1 y=-1參考以上思路，怎樣解下面類似的二元一次方程

3、組呢？歸納總結(jié)觀察系數(shù)未知數(shù)系數(shù)互為相反數(shù)時，加法消元未知數(shù)系數(shù)相等時，減法消元加減消元法未知數(shù)的系數(shù)相等或互為相反數(shù)觀察系數(shù)回代求解加減消元寫解鞏固練習(xí)觀察系數(shù)BB加減消元法3x-4y=2 2x+5y=9 怎樣解下面的二元一次方程組呢？解：由2得 6x-8y=4 由3得 6x+15y=27 x=2 y=1觀察系數(shù)統(tǒng)一系數(shù)回代求解減法消元最小公倍數(shù) -得 -23y=-23 解得 y=1 把 y=1代入得 3x-4=2 解得 x=2 原方程組的解是 寫解加減消元法3x-4y=2 2x+5y=9 怎樣解下面的二元一次方程組呢？解：由5得 15x-20y=10 由4得 8x+20y=36 x=2 y

4、=1觀察系數(shù)統(tǒng)一系數(shù)回代求解加法消元最小公倍數(shù) +得 23x=46 解得 x=2 把 x=2代入得 6-4y=2 解得 y=1 寫解 原方程組的解是 歸納總結(jié)觀察系數(shù)加減消元法未知數(shù)的系數(shù)相等或互為相反數(shù)觀察系數(shù)回代求解加減消元統(tǒng)一系數(shù)寫解鞏固練習(xí)觀察系數(shù)4x-3y=14 5x+3y=31 用加減消元法解下列方程組：（1）4x+7y=18 4x-5y=-6 （3）2x-5y=-21 4x+3y=23 （2）2x-5y=1 7x-3y=18 （4）觀察系數(shù)答案課堂小結(jié)觀察系數(shù)加減消元法未知數(shù)的系數(shù)相等或互為相反數(shù)觀察系數(shù)回代求解加減消元統(tǒng)一系數(shù)寫解將二元方程轉(zhuǎn)化為一元方程！課后思考題觀察系數(shù)33

5、x+17y=83 17x+33y=67 求解下面的二元一次方程組.目錄01輸入您的標(biāo)題020304輸入您的標(biāo)題輸入您的標(biāo)題輸入您的標(biāo)題請輸入標(biāo)題Never give up, Never lose hope. Always have faith, It allows you to cope. Trying times will pass, As they always do.Never give up, Never lose hope. Always have faith, It allows you to cope. Trying times will pass, As they always

6、 do.Never give up, Never lose hope. Always have faith, It allows you to cope. Trying times will pass, As they always do.請輸入標(biāo)題2Presentations are tools that can be used as lectures.APresentations are tools that can be used as lectures.BCPresentations are tools that can be used as lectures.DPresentatio

7、ns are tools that can be used as lectures.請輸入標(biāo)題請輸入標(biāo)題 Never give up, Never lose hope. Always have faith, It allows you to cope. Trying times will pass, As they always do. Just have patience, Your dreams will come true. Never give up, Never lose hope. Always have faith, It allows you to cope. Trying t

8、imes will pass, As they always do. Just have patience, Your dreams will come true. Always have faith, It allows you to cope. Trying times will pass, As they always do. Just have patience, Your dreams will come true. 請輸入標(biāo)題3請輸入標(biāo)題Presentations are tools that can be used as lectures.Presentations are to

9、ols that can be used as lectures.Presentations are tools that can be used as lectures.Presentations are tools that can be used as lectures.教學(xué)教學(xué)Never give up, Never lose hope. Always have faith, It allows you to cope. Trying times will pass, As they always do. Just have patience, Your dreams will com

10、e true. Never give up, Never lose hope. Always have faith, It allows you to cope. Trying times will pass, As they always do. Just have patience, Your dreams will come true. Always have faith, It allows you to cope. Trying times will pass, As they always do. Just have patience, Your dreams will come

11、true. 請輸入標(biāo)題請輸入標(biāo)題41324Presentations are tools that can be used lectures.Presentations are tools that can be used as lectures. Presentations are tools that can be used lectures.Presentations are tools that can be used as lectures. Presentations are tools that can be used lectures.Presentations are too

12、ls that can be used as lectures. Presentations are tools that can be used lectures.Presentations are tools that can be used as lectures. 請輸入標(biāo)題鞏固練習(xí)觀察系數(shù)解：由+得 9x=45 解得 x=5 把 x=5代入得 20-3y=14 解得 y=2 原方程組的解是 x=5 y=24x-3y=14 5x+3y=31 （1）鞏固練習(xí)觀察系數(shù)2x-5y=-21 4x+3y=23 （2）解：由2得 4x-10y=-42 -得 13y=65 解得 y=5x=2 y=5

13、 把 y=5代入得 4x+15=23 解得 x=2 原方程組的解是 鞏固練習(xí)觀察系數(shù)解：由-得 12y=24 解得 y=2 把 y=2代入得 4x+14=18 解得 x=1 原方程組的解是 x=1 y=24x+7y=18 4x-5y=-6 （3）鞏固練習(xí)觀察系數(shù)2x-5y=1 7x-3y=18 （4）解：由7得 14x-35y=7 由2得 14x-6y=36 -得 -29y=-29 解得 y=1x=3 y=1 把 y=1代入得 2x-5=1 解得 x=3 原方程組的解是 Never give up, Never lose hope. Always have faith, It allows you to cope. Trying times will pass, As they always do.Never give up, Never lose ho