A:1
B:2
C:3
D:4
Mr. Smith didn't go to the movie. He went swimming, ________.
一组数据有m个x1,n个x2,p个x3,那么这组数据的平均数为( )
如图所示,直角三棱镜置于空气中,已知∠A=60°,∠C=90°,一束极细单色光从AC的中点D垂直AC面入射,AD= 6 m,棱镜对该单色光的折射率n= 2 ,求: