一元二次方程$x^2=16$的根是（   ）．

                                                                                 破阵子 为陈同甫赋壮词以寄之
                                                                                                     南宋 辛弃疾
　　                                        醉里挑灯看剑，梦回吹角连营。八百里分麾下炙，五十弦翻塞外声，沙场秋点兵。
                                               马作的卢飞快，弓如霹雳弦惊。了却君王天下事，赢得生前身后名。可怜白发生！