x^2-16 = (x-4)(x+4)
a^2-100= (a-10)(a+10)
256x^2-b^2=(16x-b)(16x+b)
b^2x^2-y^2=(bx-y)(bx+y)
43^2-23^2=(43-23)(43+23)=20*66=1320
50^2-25^2=(50-25)(50+25)=25*75=1875
100^2-200^2=(100-200)(100+200)=-100*300=-30000