ab x (a - b) = ab x a + abx (-b)
                = (1 x1) x ab x a + [1 x (-1)] x ab x b
                =  1 x a² x b + (-1) x a x b²
                = a²b - ab²

(a+ b) x 7a²b²  =  a x 7a²b² + b + 7a²b² 
                     = (1 x 7) x a x a²b² + ( 1 x 7) x b x a²b²
                     = 7 x a³b² + 7 x a²b³ 
                     = 7a³b² + 7a²b3
                   
             
                

(4p² + 5p + 7) x 3p = (4p² + 3p ) + (5p x 3p) + ( 7 x 3p)
                           =  [(4 x 3) x p² x p] + [(5 x 3) x p xp ] + ( 7 x 3) x p
                            = 12p³ + 15p² + 21p

(i) 2x(3x + 5xy) = 2x x 3x + 2x x 5xy

                      = (2 x 3) X x X x + (2 x 5) X x X xy
                      = 6x² + 10x²y

(ii)     a²(2ab - 5c) = a² x 2ab + a² x (-5c)

                          = (a x 2) x a² x ab + [1 x (- 5)] x a² x c
                           = 2 x a²b + (- 5) x a²c
                           = 2a³b - 5a²c

4p x ( q + r )   =  ( 4p x q) + ( 4p x r)
                     = ( 4 x1) x p xq + ( 4 x1) x p x r
                      = 4 x pq + 4 x pr
                      = 4pq + 4 pr