阅读诗歌，回答问题。

                                                                                                            望    岳
                                                                                                              杜甫
                                                                                            岱宗夫如何？齐鲁青末了。
                                                                                            造化钟神秀，阴阳割昏晓。
                                                                                            荡胸生曾云，决眦入归鸟。
                                                                                            会当凌绝顶，一览众山小。

一个圆的直径是10cm，另一个圆的面积比这个圆的面积少16πcm²，则另一个圆的半径长为 ____m．

—He spoke ______ fast _______ I didn't follow him.

在$Rt\Delta ABC$中，$\angle C={90}^{°}$，$a=5$，$b=12$，则cosA等于（   ）