A:y=﹣2(x+1)2
B:y=﹣2(x﹣1)2
C:y=﹣2x2+1
D:y=﹣2x2﹣1
I'm surprised to hear from her. , we last met ten years ago.
如图,在△ABC中,D,E分别是AB,AC边的中点,已知BC=10,则DE等于( )