prove the following identity: cos5x - cos3x = -8sin^2x(2cos^3x - cosx)?

1 Answer

Relevance
  • 9 years ago
    Favorite Answer

    LHS=cos5x-cos3x

    =-2sin4x.sinx

    =-4sin2x.cos2x.sinx

    =-8sin^2x.cosx(2cos^2x-1)

    =-8sin^2x(2cos^3x-cosx)

    =RHS

    THUS PROVED

    USED FORMULAE>>>>>1>.coA-cosB=2sin((A+B/2)sin((B-A)/2)

    2>sin2x=2sinx.cosx(Used twice)

    3>cos2x=2cos^2x-1

    • Login to reply the answers
Still have questions? Get your answers by asking now.