几个未知数同时满足若干个条件式,求这几个未知数的某个代数式的值,我们称这类问题为条件式的求值问题．对这类问题,许多同学总是拘泥于求这些未知数的具体值后再代入相应的代数式中去求值,因而解答常常受阻．下面介绍一类条件式的求值题,其条件式 Several unknowns satisfy several conditional formulas at the same time. Find some algebraic formulae of these unknowns. We call this kind of problem a conditional evaluation problem. For this kind of problem, many students are always stuck with the specific values ​​of these unknowns and then substitute them into the corresponding algebraic expressions to evaluate them, so the answers are often blocked. The following describes a type of conditional evaluation question, its conditional expression