Solution
$$(x + y)^2$$
=$$x^2+2xy+y^2$$.
and $$(x-y)^2$$
=$$x^2-2xy+y^2$$.
so,
$$(x+y)^2-(x-y)^2$$
$$=(x^2+2xy+y^2)-(x^2-2xy+y^2)$$
$$=x^2+2xy+y^2-x^2+2xy-y^2$$
$$=4xy.$$
B is correct choice.
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