Answer:
[tex]\rm( {a}^{2} - 2ab + {b}^{2} ) \: by \: ( - {a}^{2} b)[/tex]
[tex] \displaystyle \rm( {a}^{2} \times - {a}^{2} b) - (2ab \times - {a}^{2} b) + ( {b}^{2} \times - {a}^{2} b)[/tex]
[tex] \rm{ - {a}^{4} b} + {2a}^{3} {b}^{2} - {a}^{2} {b}^{3} [/tex]