a)
[tex]3x(5x - 7) = 15 {x}^{2} - 21x[/tex]
b)
[tex] - 7x(3x - 5) = - 21 {x}^{2} + 35x[/tex]
c)
[tex]5x(3 - 5x) = 15x - 25 {x}^{2} [/tex]
d)
[tex] - 3x(7 + 5x) = -21x - 15 {x}^{2} [/tex]
