\(B=\left(y^2-x^2\right)=\left(y-x\right)\left(y+x\right)\)
\(A-B=\left(y-x\right)\left(2x-y\right)\).Do \(\left(x-y\right)⋮11\Rightarrow-1\left(x-y\right)⋮11\Rightarrow y-x⋮11\)
Đặt y - x = 11k.Ta có: \(A-B=11k\left(2x-y\right)⋮11^{\left(đpcm\right)}\)