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