A:60°
B:90°
C:120°
D:150°
青少年要顺利度过青春期,总体上要做到( )
①正确地认识自身的变化 ②不断进行心理的调适
③注意青春期生理卫生 ④保持营养的均衡和适度的运动
已知双曲线x2a2-y2b2=1a>0,b>0的左右焦点分别是F1,F2,设P是双曲线右支上一点,F1F2→在F1P→上投影的大小恰好为|F1P|,且它们的夹角为π6,则双曲线的离心率为( )
— He is kind.
His family are worried about him because they haven't __________ letters from him for a long time.