当a、b、c为何值时，代数式 有最小值？并求出这个最小值和此时以a、b、c值为边的三角形的面积．

增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。

删除：把多余的词用斜线（\）划掉。

修改：在错的词下画一横线，并在该词下面写出修改后的词。

注意：1）每处错误以及修改仅限一词；

2）只允许修改10处，多者（从第11处起)不计分。

    When we are happy, we would like share our happiness with others, making them know our enjoyment. When we are not in a good mood, we wanted to get someone whom can listen to us. Be a listener is not easy. People always complain about our worries, and a good listener should listen to them but learn to comfort them. To be a good listener can help us make good friend with others. The one who always listen to others tends to be easy-going. When he is in the trouble, his friends will be willing to help him. So let's learn to be a good listener from then on.