题目

Nowadays, phone calls and messages help us get in touch with others. It means that we seldom write letters now. But a TV show, Letters Alive(《见字如面》), is bringing back this old habit.Letters Alive invites famous actors and actresses, but there are no funny jokes or competitions. It’s just one person walking up to a microphone(麦克风) and reading a letter. The letters were written by people from different times in history. For example, in one period, they read a letter written by famous writer Xiao Hong to her younger brother in 1941. The letter shows that Xiao Hong missed her b设直线mx－y＋2=0与圆相切，求实数m的值．