A:x>13
B:x>-13
C:x≥13
D:x≥-13
要使积最大,应该怎样填?
____ ____ ____×____
What kind of structure is the sentence “The girl showed her classmates some of her family photos.”?
在△ABC中,∠C为锐角,分别以AB,AC为直径作半圆,过点B,A,C作,如图所示.若AB=4,AC=2,S1﹣S2=π4,则S3﹣S4的值是( )