题目

How often one hears children wishing they were grown up, and the old wishing they were young again! Each age has its pleasure and its pains, and the happiest person is the one who enjoys what each age gives him without wasting any time in useless regrets.     Children is a time when there are few duties to make life hard. If a child has good parents, he is fed, looked after, and loved whatever he may do. It’s impossible for him to be given so much again in his life without having to do anything in return. Besides, life is always giving new things to the child. A child finds pleasur从点A(-4,1)出发的一束光线l,经过直线l1:x-y+3=0反射,反射光线恰好通过点B(1,6),求入射光线l所在的直线方程.