(x+y)2-( )=(x-y)2.
4xy
16. ----It’s getting dark, but Mr. Johnson is still at his office.
----No surprise. Who else can _____ he does?
A.do less work than
B.work as hardly as
C.work as hard as
D.be working hardly like
有三相正弦交流电动势的交流电称为()。
A.三相交流电
B.三相电流
C.三相电压