Work Step by Step
RECALL: (1) $(a+b)(a-b) = a^2-b^2$ (2) $i^2=-1$ Use rule (1) above with $a=2$ and $b=7i$ to obtain: $=2^2 - (7i)^2 \\=4 - 49i^2$ Use rule (2) above to obtain: $=4 - 49(-1) \\=4-(-49) \\=4+49 \\=53$
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