速算
(1)0.618×999.9+0.0618
(2) 1993×1993 − 1994×1992
1994×1994 − 1995×1993
分析与解
(1)原式=0.0618×9999+0.0618
=0.0618×(9999+1)
=0.0618×10000
=618
或 原式=0.618×999.9+0.618×0.1
=0.618×(999.9+0.1)
=0.618×1000
=618
(2)原式= (1992 + 1)×1993 − (1993 + 1)×1992
(1993 + 1)×1994 − (1994 + 1)×1993
= 1992×1993 + 1993 − 1993×1992 − 1992
1993×1994 + 1994 − 1994×1993 − 1993
= 1
1
= 1