如果一个多边形的内角和等于360度,那么这个多边形的边数为( )
A.4
B.5
C.6
D.7
∵(n-2)•180°=360°,
解得n=4,
∴这个多边形为四边形.
故选A.
如图14所示为一作简谐运动的弹簧振子的振动图像,请根据图像,
⑴写出该振子正弦函数表示的振动方程。
⑵算出t1=0.5s时刻振子对平衡位置的位移。
⑶求出振子在6s内通过的路程。
It was _________that Miss Wang had been to California and there she met Dr. White __________, who became her husband later.
A.the first time, the first time
B.the first time, for the first time
C.for the first time, for the first time
D.for the first time, the first time