简便计算几道.(80+1/78)×79(224+1/222)×1/2231/2+1/6+1/12+……1/90
2个回答

(80+1/78)×79

=80X79+1/78x79

=80X(80-1)+1/78X(78+1)

=80X80-80X1+1/78X78+1/78X1

=640-80+1+1/78

=561+1/78

=561又1/78

(224+1/222)×1/223

=(223+1+/222)X1/223

=【223+(1+1/222)】X1/223

=(223+223/222)X1/223

=223X1/223+223/222X1/223

=1+1/222

=1又1/222