A:密度
B:质量
C:半径
D:自转周期
如图,已知AB∥CD∥EF,AD:AF=3:5,BE=12,那么CE的长等于( )
已知a、b、c为某一直角三角形的三条边长,c为斜边.若点(m,n)在直线ax+by+2c=0上,则m2+n2的最小值是____
— Excuse me, may I use your bicycle? ______ is broken.— Certainly. But remember to return it before lunch.