ta có a+b=9
=>(a+b)^2=81
=>(â-b)^2+4ab=81
=>(a-b)^2=80-4.20
=>(a-b)^2=80-81
=>(a-b)^2=(-1)
mà a<b nên a-b<0
=> a-b = -1
vậy (a-b)^2011 =(-1) ^ 2011=(-1)
Ta có : \(a+b=9\Leftrightarrow a^2+b^2+2ab=81\Rightarrow a^2+b^2+40=81\)
\(\Rightarrow a^2+b^2=41\Rightarrow a^2+b^2-2ab=41-40=1\)
\(\Leftrightarrow\left(a-b\right)^2=1\Rightarrow a-b=-1\left(a< b\right)\)
\(\Rightarrow\left(a-b\right)^{2011}=-1^{2011}=-1\)