Answer
$7~cos(-5β)~sin~3β=\frac{7}{2}(-sin~2β+sin~8β)$
Work Step by Step
$7~cos(-5β)~sin~3β=7(\frac{1}{2})[sin(-5β+3β)-sin(-5β-3β)]=\frac{7}{2}[sin(-2β)-sin(-8β)]=\frac{7}{2}(-sin~2β+sin~8β)$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.