一、设比值法例1解方程组(?) 解析:本题中的第三个方程是比例式,根据比例式的性质可设x= 2k(k≠0,本文下同),z=3k,那么由原方程组可得 (?) 故原方程组的解为(?) 注意:在方程组中,某方程是比例式时,一般采用设比值法．二、消常数项法例2 解方程组(?) 解析:由①+②,得x=y. 把x=y代入①,得y=1．故原方程组的解为(?) 注意:方程组中两个方程的常数项互为相反数,故可采取消除常数 First, set the ratio of the law to solve equations (?) Analysis: The third equation in this question is proportional, according to the nature of the ratio can be set x = 2k (k ≠ 0, the same below), z = 3k, then From the original equations available (?) So the solution of the original equations is (?) Note: In the equations, when an equation is proportional, the ratio is usually used to set the ratio method. Second, eliminate the constant term of the law 2 solution equations (?) Analysis: From 1 + 2, get x = y. Substitute x = y, get y = 1. Therefore, the solution of the original equations is (?) Note: The constant terms of the two equations in the system of equations are inverse numbers, so the elimination constant can be used.