Question

sina+sin2a=0and cos2a+cos4a=?

Answer 1

$sin \: a \: + sin \: 2a \: = 0 \\ sin \: a(1 + 2) = 0 \\ sin \: a = 0 \\ so \: a = 0 \\ cos \: 2a + cos \: 4a \\ = cos \: 0 + cos \: 0 \\ = 1 + 1 \\ = 2$
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