学习了一次方程组以后，可以用它来解许多初中数学竞赛试题．试举几例说明．例1若是关于x、y的二元一次方程，则兮的值等于（1997年“希望怀”全国数学邀请赛初一试题）解由二元一次方程的定义，得两式相加，得’的解，则a与c的关系是（（1997年山东省初中数学竞赛试题”由此得 After studying a system of equations, you can use it to solve many junior high school math contest questions. Give a few examples. Example 1 If it is a binary equation with x and y, then the value of 兮 is equal to (the first question of the “Hope for Hope” National Mathematical Invitational Tournament in 1997). The solution is defined by a binary equation, and the two equations are added together. Solution, the relationship between a and c is ((1997 Shandong junior high school mathematics competition test questions)