。
39×98+78=39x(100-2)+78=39x100-39x2+78=3900-78+78=3900
=39x98+39x2=39x(98+2)=39x100=3900
39×98+78=39x98+39x2=39x(98+2)=39x100=3900
39×98+78怎么简便计算