325. La expresión ${{\left( z-y \right)}^{2}}-{{\left( z+y \right)}^{2}}$ es igual a

a) 0

b) $-2{{y}^{2}}$

c) $-4yz$

Operando:

${{\left( z-y \right)}^{2}}-{{\left( z+y \right)}^{2}}\ \ =\ \ \left( {{z}^{2}}-2zy+{{y}^{2}} \right)-\left( {{z}^{2}}+2zy+{{y}^{2}} \right)\ \ =$

$=\ \ {{z}^{2}}-2zy+{{y}^{2}}-{{z}^{2}}-2zy-{{y}^{2}}\ \ =\ \ -4zy$