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

a) $2{{x}^{2}}+2{{y}^{2}}$

b) $2{{x}^{2}}$

c) $2x\left( x+y \right)$

Operando:

${{x}^{2}}-{{y}^{2}}+{{\left( x+y \right)}^{2}}\ \ =\ \ {{x}^{2}}-{{y}^{2}}+\left( {{x}^{2}}+2xy+{{y}^{2}} \right)\ \ =$

$=\ \ {{x}^{2}}-{{y}^{2}}+{{x}^{2}}+2xy+{{y}^{2}}\ \ =\ \ 2{{x}^{2}}+2xy\ \ =\ \ 2x\left( x+y \right)$