- Who did Mary dream about one night? ( )
- __________________
A:Dick.
B:At seven old years old.
C:Keep a diary.
用一水平力F将两铁块A和B紧压在竖直墙上而静止,如图所示,对此,下列说法中正确的是( )
(1)若(x2﹣1)+(x2+3x+2)i是纯虚数(i为虚数单位),求实数x的值;
(2)已知z的共轭复数为z-,且(z+z-)2=3zz-·i=4-12i(i为虚数单位),求复数z.
△ABC中,AB=AC,∠BAC=30°,△ABC的面积为49,P为直线BC上一点,PE⊥AB,PF⊥AC,CH⊥AB,垂足分别为E,F,H.若PF=3,则PE=____
“黄梅时节家家雨”中的“雨”属于( )