TrigonometryChallengeSum, Difference, and Multiple-Angle Formulas ShareSum, Difference, and Multiple-Angle Formulas · Challenge problemEvaluate cos20∘cos40∘cos80∘\cos 20^\circ\cos 40^\circ\cos 80^\circcos20∘cos40∘cos80∘ by telescoping with a well-chosen sine.Check Show answer Walk through it step by step Practice more like this Review this concept