Question

5．若|3x+2y+7|+|5x-2y+1|=0，則x，y的值是（　�。�

• A． $\left\{\begin{array}{l}{x=1}\\{y=1}\end{array}\right.$
• B． $\left\{\begin{array}{l}{x=2}\\{y=\frac{1}{2}}\end{array}\right.$
• C． $\left\{\begin{array}{l}{x=-1}\\{y=-2}\end{array}\right.$
• D． $\left\{\begin{array}{l}{x=-2}\\{y=-\frac{1}{2}}\end{array}\right.$

Answer 1

分析 先根據(jù)非負(fù)數(shù)的性質(zhì)列出關(guān)于x、y的二元一次方程組，再利用加減消元法求出x的值，利用代入消元法求出y的值即可．

解答 解：∵|3x+2y+7|+|5x-2y+1|=0，
∴$\left\{\begin{array}{l}3x+2y+7=0①\\ 5x-2y+1=0②\end{array}\right.$，
①+②得，8x+8=0，解得x=-1，
把x=-1代入①得，-3+2y+7=0，解得y=-2，
∴方程組的解為$\left\{\begin{array}{l}x=-1\\ y=-2\end{array}\right.$．
故選C．

點評 本題考查的是解二元一次方程組，熟知解二元一次方程組的加減消元法和代入消元法是解答此題的關(guān)鍵．