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(sin u cos 2u)/(cos^(3)u)

sinucos2ucos3u \frac{\sin u \cos 2 u}{\cos ^{3} u}

Full solution

Q. sinucos2ucos3u \frac{\sin u \cos 2 u}{\cos ^{3} u}
  1. Apply double angle formula: Apply the double angle formula for cosine.\newlineThe double angle formula for cosine is cos(2u)=cos2(u)sin2(u)\cos(2u) = \cos^2(u) - \sin^2(u).
  2. Substitute formula into expression: Substitute the double angle formula into the original expression.\newlineReplace cos(2u)\cos(2u) in the original expression with (cos2(u)sin2(u))(\cos^2(u) - \sin^2(u)) to get sinu(cos2(u)sin2(u))cos3u\frac{\sin u \cdot (\cos^2(u) - \sin^2(u))}{\cos^{3}u}.
  3. Distribute sinu\sin u: Distribute sinu\sin u over the terms inside the parentheses. Multiply sinu\sin u with both cos2(u)\cos^2(u) and sin2(u)-\sin^2(u) to get (sinucos2(u)sin3(u))/(cos3u)(\sin u \cdot \cos^2(u) - \sin^3(u))/(\cos^{3}u).
  4. Split fraction into two: Split the fractions" target="_blank" class="backlink">fraction into two separate fractions. Divide both terms in the numerator by cos3u\cos^{3}u to get (sinucos2(u))/(cos3u)(sin3(u))/(cos3u)(\sin u \cdot \cos^2(u))/(\cos^{3}u) - (\sin^3(u))/(\cos^{3}u).
  5. Simplify the fractions: Simplify the fractions.\newlineThe first term simplifies to sinu/cosu\sin u/\cos u because one cosu\cos u in the numerator and denominator cancels out. The second term simplifies to sin3(u)/cos3(u)-\sin^3(u)/\cos^3(u), which is tan3(u)-\tan^3(u).
  6. Combine simplified terms: Combine the simplified terms. The expression now is tanutan3(u)\tan u - \tan^3(u).

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