已知，二次型的秩为2，(I)求实数a的值；(II)求正交变换x=Qy将f化为标准形.
Mr.Smithisingoodhealthnowforitisquitealongtimesincehe__________.
______progressyouhavemakethisterm!
进行行情预测应遵循的基本原则包括()
WhenBobwokeuphefoundhimselfinhospital,buthedidnt__________.
TheGreatWallinChinaisoneofthefew_____objectsontheearth_____fromthemoon.
