139x137/138+137x1/138奥数减算：1993x1994-1/1993+1992x1994
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139x137/138+137x1/138奥数减算：1993x1994-1/1993+1992x1994
139x137/138+137x1/138
奥数减算：1993x1994-1/1993+1992x1994
139x137/138+137x1/138奥数减算：1993x1994-1/1993+1992x1994
139x137/138+137x1/138
=(138+1)x(138-1)/138+137x1/138
=(138^2-1)/138+137x1/138
=138^2/138+(137-1)/138
=138+136/138
=138+68/69
=138又69分之68
1993x1994-1/1993+1992x1994
分子=1993x(1993+1)-1
=1993^2+1993-1
=1993^2+1992
分母=1993+(1993-1)x(1993+1)
=1993+1993^2-1
=1993^2+1992
所以1993x1994-1/1993+1992x1994=1
139x137/138+137x1/138
=(138+1)x(138-1)/138+137x1/138
=(138^2-1)/138+137x1/138
=138^2/138+(137-1)/138
=138+136/138
=138+68/69
=138又69分之68
1993x1994-1/1993+1992x1994
分子=1...
全部展开
139x137/138+137x1/138
=(138+1)x(138-1)/138+137x1/138
=(138^2-1)/138+137x1/138
=138^2/138+(137-1)/138
=138+136/138
=138+68/69
=138又69分之68
1993x1994-1/1993+1992x1994
分子=1993x(1993+1)-1
=1993^2+1993-1
=1993^2+1992
分母=1993+(1993-1)x(1993+1)
=1993+1993^2-1
=1993^2+1992
所以1993x1994-1/1993+1992x1994=1
收起
(1)139X137/138+137/138=(139+1)x137/138
=140x137/138=140x(1-1/138)=140-140/138
=138又68/69
(2)原式=1993x1994-1/1993+1993x1993-1
=1993x1994-1993x1993-1/1993-1
=1993x(1994-1993)-1/1993-1
=1993-1/1993-1
=1991又1992/1993