Work Step by Step
RECALL: (1) $a(b+c) = ac + bc$ (2) $i^2=-1$ Use rule (1) above to obtain: $=5i(4) + 5i(7i) \\=20i + 35i^2$ Use rule (2) above to obtain: $=20i + 35(-1) \\=20i +(-35) \\=-35 +20i$
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