1) ( Х - 2 )*( Х - 3 ) = х^2 - 3х - 2х + 6 = х^2 - 5х + 6 ;
2) ( 7t + k )*( t + 7k ) = 7t^2 + 49tk + tk + 7k^2 = 7t^2 + 7k^2 + 50tk ;
3) 2a * ( 3a - 5 ) - ( a - 3 )*( a - 7 ) = 6a^2 - 10a - ( a^2 - 7а - 3а + 21 ) = 6а^2 - 10а - а^2 + 10а - 21 = 5а^2 - 21