A6. Calculate $\left((\sqrt{2}+1)^{7}+(\sqrt{2}-1)^{7}\right)^{2}-\left((\sqrt{2}+1)^{7}-(\sqrt{2}-1)^{7}\right)^{2}$.
A) 2
B) 4
C) $8 \sqrt{2}$
D) 128
E) 512
A6. B) 4 Given $a=(\sqrt{2}+1)^{7}$ and $b=(\sqrt{2}-1)^{7}$. Then the given expression is equal to

$$
(a+b)^{2}-(a-b)^{2}=4 a b=4(\sqrt{2}+1)^{7}(\sqrt{2}-1)^{7}=4((\sqrt{2}+1)(\sqrt{2}-1))^{7}=4 \cdot 1^{7}=4
$$