Question

用平方差公式简便计算

1.999^2-998^2
2.(81又1/2)^2-(78又1/2)^2

Answer 1

1.999^2-998^2
=(999-998)*(999+998)
=1*(1000-1+1000-2)
=2000-3
=1997
2.(81又1/2)^2-(78又1/2)^2
=(81+1/2)^2-(78+1/2)^2
=(81+1/2-78-1/2)(81+1/2+78+1/2)
=3*(159+1)
=3*160
=480

Answer 2

1.
999^2-998^2
=(999+998)(999-998)
=1997
2.
(81又1/2)^2-(78又1/2)^2
=(81又1/2+78又1/2)(81又1/2-78又1/2)
=160*3
=480