$$( 2 \sqrt { 2 } + 7 \sqrt { 7 } ) ( 2 \sqrt { 2 } - 7 \sqrt { 7 } )$$
$-335$
$$\left(2\sqrt{2}\right)^{2}-\left(7\sqrt{7}\right)^{2}$$
$$2^{2}\left(\sqrt{2}\right)^{2}-\left(7\sqrt{7}\right)^{2}$$
$$4\left(\sqrt{2}\right)^{2}-\left(7\sqrt{7}\right)^{2}$$
$$4\times 2-\left(7\sqrt{7}\right)^{2}$$
$$8-\left(7\sqrt{7}\right)^{2}$$
$$8-7^{2}\left(\sqrt{7}\right)^{2}$$
$$8-49\left(\sqrt{7}\right)^{2}$$
$$8-49\times 7$$
$$8-343$$
$$-335$$
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