Question

помогите пятое!!!!!!!

Answer 1

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Answer 2

$frac{sina+sin3a}{cosa+cos3a}\\ sina+sinb=2sinfrac{a+b}{2}*cosfrac{a-b}{2}\ cosa+cosb=2cosfrac{a+b}{2}*cosfrac{a-b}{2}\\ sina+sin3a=2sin2a*cosa\ cosa+cos3a=2cos2a*cosa\ \ frac{2sin2a*cosa}{2cos2a*cosa}=tg2a$