Answer:
x²+y²+z²+2xy-2yz-2zx
Step-by-step explanation:
{(x+y)-z}^2
=(x+y)²-2(x+y)z+z²
=x²+2xy+y²-2zx-2yz+z²
=x²+y²+z²+2xy-2yz-2zx
