4/5-4/5X5/6
=(1-5/6)X4/5
=1/6X4/5
=2/15
3/7X3/21X21X7
=3/7x7×(3/21×21)
=3×3
=9
4/15X2/19+17/19X4/15
=4/15X(2/19+17/19)
=4/15X1
=4/15
4/5-4/5X5/6
=4/5×(1-5/6)
=4/5×1/6
=2/15
3/7X3/21X21X7
=(3/7×7)×(3/21×21)
=3×3
=9
4/15X2/19+17/19X4/19没有简便方法,是不是抄错题了?
①=4/5*(1-5/6)=4/5*1/6=2/15
②=3/7*7*(3/21*21)=3*3=9
③=4/19*(2/15+17/19)