五年級(下)奧數(shù)第2講二元一次方程組的解法

1、百匯教育五年級（下冊）奧數(shù) 第2講：二元一次方程組的解法第2講 二元一次方程組的解法 搜集整理：百匯教育數(shù)學組陳超【知識要點】1 二元一次方程組的有關概念 （1）二元一次方程：含有兩個未知數(shù)，并且含有未知數(shù)的項的次數(shù)都是1的整式方程叫做二元一次方程。例如3x4y9。 （2）二元一次方程的解集：適合一個二元一次方程的每一對未知數(shù)的值，叫做這個二元一次方程的一個解。對于任何一個二元一次方程，令其中一個未知數(shù)取任意一個值，都能求出與它對應的另一個未知數(shù)的值。因此，任何一個二元一次方程都有無數(shù)多個解。由這些解組成的集合，叫做這個二元一次方程的解集。 （3）二元一次方程組及其解：兩個二元一次方程合在一起

2、就組成了一個二元一次方程組。一般地，能使二元一次方程組的兩個方程左右兩邊的值都相等的兩個未知數(shù)的值，叫做二元一次方程組的解。 2 二元一次方程組的解法 （1）代入消元法：在二元一次方程組中選取一個適當?shù)姆匠蹋瑢⒁粋€未知數(shù)用含另一個未知數(shù)的式子表示出來，再代入另一個方程，消去一個未知數(shù)得到一元一次方程，求出這個未知數(shù)的值，進而求得這個二元一次方程組的解，這種方法叫做代入消元法。 （2）加減消元法：兩個二元一次方程中同一未知數(shù)的系數(shù)相反或相等時，將兩個方程的兩邊分別相加或相減，從而消去這個未知數(shù)，得到一個一元一次方程，這種求二元一次方程組的解的方法叫做加減消元法。代入消元法將在七年級數(shù)學（上冊&#

3、183;上?？萍汲霭嫔纾┙滩闹袑W習到。本次課，我們主要講解加減消元法。【典型例題】用加減消元法解下列方程組： 例1、 x5y 0 3x5y 16 解：由得：x3x16 即4x16 所以x4把x4代入得：3×45y16 解得 y0.8所以原方程組的解為 x4 y0.8例2、 2x2y11 2x7y36 解：由得：7y2y3611 即5y25 所以y5把y5代入得：2x2×511 解得 x0.5所以原方程組的解為 x0.5 y5例3、 4x2y5 4x9y16 解：由得：9y（2y）165 即9y2y11 解得 y1把y1代入得：4x2×15 解得 x所以原方程組的解

4、為 x y1例4、 4x6y8 4x3y17 解：由得：（3y）（6y）178 即3y6y9 解得 y3把y3代入得：4x6×38 解得 x6.5所以原方程組的解為 x6.5 y3例5、 2x3y5 3x9y12 解：由×3得：6x3x1512 即9x27 解得 x3把x3代入得：3×39y12 解得 y所以原方程組的解為 x3 y例6、 3x2y8 4x3y5 解：由×4×3得： （8y）（9y）3215 即8y9y17 解得 y17把y17代入得：4x3×175 解得 x14所以原方程組的解為 x14 y17【技能測試】（1） （

5、2） （3） （4） （5） （6）【拓展提高】（1） （2）（3） （4） （5） （6） 清水混凝土的配合比設計中，要針對當?shù)厮?、砂石、外摻料及外加劑等原材料影響混凝土質量的多種因素進行分析，確定主要控制因素，并從經濟性和使用要求綜合考慮，優(yōu)選出符合生產條件的最優(yōu)方案組合。obstacles, correcting misunderstandings, advocate good cadre style. 2, adhere to the scientific decision-making and democratic decision-making decision-making l

6、aw. Correctly handle to ensure that government decrees and based on the actual creative work, giving full play to subjective initiative, put an end to implement the conference meeting, to document the implementation of documents etc. Improve the scientific and democratic decision-making mechanism, i

7、mprove and implement the decision to solicit the views of experts, the public hearing system. Improve the important decision of risk assessment mechanism and legal review mechanism. 3, to promote team unity. Uphold and improve the system of annual party book talk heart to heart, mind and Party membe

8、rs, Party members to exchange each other not less than 2 times. The implementation of sound team democratic life system, consolidate and enhance the party's mass line educational practice will promote the achievement of the topic of democratic life, criticism and self-criticism normalization, a

9、long-term. Adhere to the party on the basis of the principle of unity, enhance internal communication, strengthen internal supervision, self Sleep maintenance team collective image and authority. (three) to ensure the execution is not strong or disguised to resist government decrees issues. Individu

10、al Bureau leadership team members lack of learning political theory system, not from the objective reality, not with the party's interests above all the principles to deal with personal problems. In the specific work safety supervision in the execution is not strong, in the implementation of the

11、 decision to deploy the discount, make choices, engage in work, the implementation of the agreement, uncomfortable is not performed, open or disguised to resist, the lack of subject consciousness of the party organization, the lack of resist in society all kinds of bad habits and unwholesome tendenc

12、ies of courage Gas and courage. Such as the liability insurance of safe production work, individual leaders that have someone arrested, and no funding, not in the global chess perspective to the countryside to carry out daily inspection, found none of my business acceptance of the resumption of prod

13、uction in an armchair, with a pen, indifferent. Corrective measures: (LED Leadership: Luo Mingjun, rectification time: before September 25th, insist for a long time) 1, to strengthen the sense of responsibility, work to solve the lack of decent occupation explain away, conduct problems. To establish the overall concept, eliminate departmentalism. Strict assessment and accountability, to solve the spiritual slack, nianqingpazhong, status quo, To establish and perfect the muddle along and other issues. Bureau staff conduct work regulations, standardize the behavior of personnel. 2, strengt