Question

Tính nhanh

A = ( 1999/2011 - 2011/1999 ) - ( -12/1999 - 12/2011 )

B = 2/5 + [ 3/11 + (-2)/5 ]

 

Answer 1

A=1999/2011-2011/1999-(-12/1999)-12/2011

Answer 2

A = ( 1999/2011 - 2011/1999 ) - ( -12/1999 - 12/2011 )

=1999/2011-2011/1999+12/1999+12/2011

=(1999/2011+12/2011)-(2011/1999-12/1999)

=1-1

=0

Vậy A=0

B = 2/5 + [ 3/11 + (-2)/5 ]

=[2/5+(-2/5)]+3/11

=0+3/11

=3/11