1 995 + 1995 × 1996 - 1997 × 1994 = 1 997
= 1 995 × ( 1 + 1 996 ) - 1 997 × 1 994 =
= 1 995 × 1997 - 1 997 × 1 994 =
= 1 997 × ( 1 995 - 1 994 ) =
= 1 997 × 1 =
= 1 997
__________________________________
b)
1 997 × 109 - 199700 - 1997 × 7 - 1997 = 1 997
= 1 997 × ( 109 - 100 - 7 - 1 ) =
= 1 997 × ( 9 - 7 - 1 ) =
= 1 997 × 1 =
= 1 997