Apply double angle formula: Apply the double angle formula for cosine.The double angle formula for cosine is cos(2u)=cos2(u)−sin2(u).
Substitute formula into expression: Substitute the double angle formula into the original expression.Replace cos(2u) in the original expression with (cos2(u)−sin2(u)) to get cos3usinu⋅(cos2(u)−sin2(u)).
Distribute sinu: Distribute sinu over the terms inside the parentheses. Multiply sinu with both cos2(u) and −sin2(u) to get (sinu⋅cos2(u)−sin3(u))/(cos3u).
Split fraction into two: Split the fractions" target="_blank" class="backlink">fraction into two separate fractions. Divide both terms in the numerator by cos3u to get (sinu⋅cos2(u))/(cos3u)−(sin3(u))/(cos3u).
Simplify the fractions: Simplify the fractions.The first term simplifies to sinu/cosu because one cosu in the numerator and denominator cancels out. The second term simplifies to −sin3(u)/cos3(u), which is −tan3(u).
Combine simplified terms: Combine the simplified terms. The expression now is tanu−tan3(u).
More problems from Sin, cos, and tan of special angles