Question

4．若方程組$\left\{\begin{array}{l}{ax+y=0}\\{2x+by=6}\end{array}\right.$的解是$\left\{\begin{array}{l}{x=1}\\{y=-2}\end{array}\right.$，則a+b=（　�。�

• A． 2
• B． -2
• C． 0
• D． 4

Answer 1

分析 根據(jù)方程組$\left\{\begin{array}{l}{ax+y=0}\\{2x+by=6}\end{array}\right.$的解是$\left\{\begin{array}{l}{x=1}\\{y=-2}\end{array}\right.$，可以求得a、b的值，從而可以求得a+b的值．

解答 解：∵方程組$\left\{\begin{array}{l}{ax+y=0}\\{2x+by=6}\end{array}\right.$的解是$\left\{\begin{array}{l}{x=1}\\{y=-2}\end{array}\right.$，
∴$\left\{\begin{array}{l}{a-2=0}\\{2-2b=6}\end{array}\right.$，
解得，a=2，b=-2，
∴a+b=2+（-2）=0，
故選C．

點評 本題考查二元一次方程組的解，解題的關(guān)鍵是明確題意，找出所求問題需要的條件．