Question

17．方程组$\left\{\begin{array}{l}{3x+4y=5}\\{-7x+8y=-16}\end{array}\right.$的解是（　　）

• A． $\left\{\begin{array}{l}{x=2}\\{y=-0.25}\end{array}\right.$
• B． $\left\{\begin{array}{l}{x=-1}\\{y=-0.5}\end{array}\right.$
• C． $\left\{\begin{array}{l}{x=1}\\{y=0.5}\end{array}\right.$
• D． $\left\{\begin{array}{l}{x=-5.5}\\{y=4}\end{array}\right.$

Answer 1

分析 方程组利用加减消元法求出解即可．

解答 解：$\left\{\begin{array}{l}{3x+4y=5①}\\{-7x+8y=-16②}\end{array}\right.$，
①×2-②得：13x=26，
解得：x=2，
把x=2代入①得：y=-0.25，
则方程组的解为$\left\{\begin{array}{l}{x=2}\\{y=-0.25}\end{array}\right.$，
故选A

点评 此题考查了解二元一次方程组，利用了消元的思想，消元的方法有：代入消元法与加减消元法．