№670
1) (х+2)²(х-х+1)= х²+4х+4
2) (а-2)(а²+2а+4)= а³-2³
3) (m/2-2n)(m²/4+nm+4n²)= m/2³-2n³
№671
1) (3ав)³ = (3*1/2*4)³= 6³= 216
2) -(1/5хуz)² = - (1/5* (-2)* (-5)* 7/4)²= - ( 7/2)²= -49/4
№ 672
1) 15х/20у= 3х/4у
2) 6ху/8у²= 3х/4у
3) 2m²/3mn= 2m/3n
4) 24а³/ 56а²в = 3а/7в