( x - 3)(x - 7) - 2x(3x - 5) = x^2 - 10x + 21 - 6x^2 + 10x = - 5x^2 + 21
4a(a- 2) - ( a - 4)^2 = 4a^2 - 8a - ( a^2 - 8a + 16)= 4a^2 - 8a - a^2 + 8a - 16=
= 3a^2 - 16
2( m + 1)^2 - 4m = 2(m^2 + 2m + 1) - 4m = 2m^2 + 4m + 2 - 4m =
= 2m^2 + 2 = 2(m^2 + 1)