(x-y+z)(x+y-z)
=[x-(y-z)][x+(y-z)]
=x²-(y-z)²
=x²-y²+2yz-z²
1/2(1+1/2)(1+1/4)(1+1/16)
=(1-1/2)(1+1/2)(1+14)(1+1/16)
=(1-1/4)(1+1/4)(1+1/16)
=(1-1/16)(1+1/16)
=1-1/256
=255/256