解方程:x2+4x+2=0.
∵x2+4x+2=0
∴x2+4x=-2
∴x2+4x+4=-2+4
∴(x+2)2=2
∴x=-2±2
∴x1=-2+2,x2=-2-2
Not until I began to work _____ how much time I had wasted [ ]
A. didn't I realize
B. I didn't realize
C. did I realize
D. I realized
心房颤动时f波的频率约为()
A.300~600次/分
B.250~500次/分
C.350~600次/分
D.100~200次/分
E.200~350次/分