英语翻译14.In the,a middle school football conference,each team

这个应该是题目做法解析吧,但前一个和后一个都有不全的地方.I wonder why……
大意为：
14.一个中学搞足球比赛,每个队只跟别的每一个队比赛一次.如果在2012赛季总共比了21次,请问有多少个队参加了这次比赛?
（14.In the,a middle school football conference,each team plays every other team exactly once.If a total of 21 conference games were played during the 2012 season,how many teams were members of the BIG N conference?）
这个问题和握手问题非常相似.我们常用这个公式去找出比赛的次数（或是握手的）.现在我们反着用这个公式.
因此我们有了这个方程的解,我们解出队伍的数量为 （为什么就没了啊!）
（This problem is very similar to a handshake problem.We use the formula to usually find the number of games played (or handshakes).Now we have to use the formula in reverse.
So we have the equation Solving,we find that the number of teams in the BIG N conference is .）
14.14.在BIG.N中,一个中学搞足球比赛,每个队只跟别的每一个队比赛一次.如果在2012赛季总共比了21次,请问有多少个队参加了这次比赛?
（14.In theBIG N,a middle school football conference,each team plays every other team exactly once.If a total of 21 conference games were played during the 2012 season,how many teams were members of the BIG N conference?）
这个问题跟握手问题非常相似.我们常用公式n(n-1)/2去找比赛的次数.现在我们反着用这个公式.n(n-1)/2=21