题目

.计算：（1）             （2） （3）                            （4）                       （6）  答案： （1）             （2）=                                      = 5（3）                      （4）  =  3                                   =  -6                      （6）     = 1                                     若P为l：x－y＋3＝0上动点，过P作(x＋2)2＋(y＋2)2＝1的切线，则所得切线长的最小值是________．